This only works in PvP where there’s only one difficulty and where the average winrate is 50%, so it’s easy to measure how good a player is relatively to others.
In PvE with 3 random affixes in 8 dungeons and a dozen class setups it’s impossible to calibrate such a system.
Plus by the community’s logic only the healer should lose rating because it’s always their fault.
Nobody would touch that system for PvE.
Oh, you somehow decided that I excluded myself before? No-no, it would be weird, like it’s weird and unwise for you to make such an assumption in my regard. I actually acknowledged this already with a statement that our opinions aren’t carrying much worth – and also added a warning about trying to make far-reaching conclusions from what people are saying there. Obviously, me included. 
I’m not here to fix anything, only to share opinions, very personal and extremely subjective. I’m okay with that. If you are here to listen to them or not, if you being serious or not about that, this is of very minor consequence for me.
Rio is MMR in this case, but this shouldn’t be it. I will provide you with one short and simple example on how random matchmaking could differentiate itself from the system we have now with another approach to raid buffs and party-wide utility in m+. I’m not not here to defend this particular solution because there could be many like that which can spark up the RMM M+ engine, and it’s not for us (or for me, at least) to decide which would work best.
So, currently, it is considered detrimental to your success in higher key levels to make a group without a source of Blood Lust, at least one possibility for battle ressurection, a shorter kick, and so on. Hence, while making a decision about who you will grab with you into the dungeon, you limit your choice to classes that bring such utility. But what about if in RMM M+ all this would come for granted?
If you no longer have any power over bringing that particular shaman with you or not to cater for specific mechanics, their value is no longer being determined by Blood Lust or curse dispel that they bring. Instead, how about if all random groups will possess an ability to Blood Lust in a manner not too different from how Ultimates work in FF? This extra ability would be always in possession of any tank, for example, as they are usually on the routing duty.
Then, instead of BRs, you will have an option for limited numbers of ressurections engraved into spellbooks of all DPS players. All healers would gain an ability to dispel everything while inside this RM+ dungeon. All mobs and bosses are constantly under effects of DHs’ Brand, Monks’ Touch, Hunters’ Mark, and so on. There’re always free Heartstones at the entrance. And you always have something similar to Priest buff, and dungeons are rebalanced and accustomed to this. All kicks are mid-range and of equal cooldown. And so on.
You cut everything from the picture that isn’t your ability to act, to plan, to make a decision.
Let’s remove classes and give healers a button called “heal”, DPS one called “pew” and tanks, I dunno “ouch”.
Might as well get instant loot at this point. And delete classes as a whole. We do not need them
The story of how PvP got into the sad state its in, especially for healers… Should be a warning for expressing “opinions” and expecting awe in return.
Nobody wants this, as you have seen. You might be entitled to your opinoin OK. But nobody wants this after having seen what happened with PvP.
So keep talking. I will make sure that for every post about MMR in M+ there is, there are 10 others saying its a stupid idea.
Just in case Blizz reads this. As they did with PvP and ruined that game mode.
All these complaints are 100% class and dungeon design. Im the first to complain about the state of dispells and such.
But its totally unrelated to MMR or Solo quew.
In addition, there is a simpler solution than to homogenize every class: Just make hard-hiting / hard stake mechanics unavoidable.
No more Mass Dispelling a boss mechanic allowing you to cheese it. No more physical damage dots, where plate wearers dont even notice it but cloth weares are murdered by it…
Simple things. DONE.
No need for new game modes.
Was going to ask: who is forcing you to?
But that would’ve been unfair to you because if players can use the dungeon finder for M+ no one would do keys; resulting in you being forced to queue with randoms.
So it makes sense why you are against it.
Not from the game, my good people. From this stand-alone mode, one smaller part of the game. Because we assume that in this mode we won’t be able to make any decisions at all besides what we ourselves can do. Thus, it would be more fun for Blizzard to cover there for us. You won’t lose your ability to push (if you’re actually pushing and trying any content where decisions actually matter) in proper M+ environment, if you like it! I’m certainly not here to trade one for another, and I would like doing both things equally like I like Solo Shuffles and I like Random Battlegrounds.
No, I’m seeing the opposite. More and more. People want it. And I will support this interest of theirs.
So you want whole different mode. Not queues and MMR for m+. Important distinction
So you want to have 1 tank, 1 dps and 1 heal class. and remove all utility or every has the same. Same interrupt, same stun, same cc. Why no more physical damage dots while you can also remove those or defensive those just like magic?
OK. Well this ruined PvP. It WILL ruin M+ as well.
Simply because its not a solution to the problem. And people are idiots:
And the list goes on…
This whole discussion is void tbh. The problem is only the top 1% of DPS gets into M+ because there’s so many of them compared to other roles that people can cherry pick
People claim that an automated round-robin system would be more fair as every DPS would have equal wait time.
This is exactly what happened in PvP, how are the DPS queues over there?
If blizz wants to fix this they need to make healing as fun for the average player as DPSing. That’s “all”.
Oh, i am the same… i rather be at work for another 10min and buy a token, than farm the gold… but still, my faith in bliz is pretty much nonexistent with stupid choices 
Are you dense? I never said that… There is a difference between a CORE mechanic, and an auxiliary one.
Let me put it simple:
Do you think its good for M+ to allow a single class (priest) to completly cheese one of the hardest and most anoying affixes (Bursting)? Like what happened in S2?
It has nothing to do with class flavour. Priest can dispell diseases and I cant. Sure, it adds fluff. But bursting? NO. Nobody should be able to cheese that.
Do you think its smart to allow only 1 class (Priest) to Mind Soothe packs while a rogue cant shroud it? You can either skip the pack or you cant. But not “1 class can chease a dungeon and nobody else can cheese the dungeon”…
And I emphasize CHEESING. Not interacting. Which is different.
Get my point now?
I think their choices are mainly to appeal to the people who spend the most money, so we should be safe
Yes and no. Like I said before, it won’t work if you just tie MMR random queueing to our current system. As someone who actually does like pushing and doing slightly harder content than most casuals, I acknowledge it responsibly: won’t work, won’t happen. So, changes are needed. Redesigns, new approaches, new ideas. What stays, is that you are still doing relatively harder dungeon content with randomly assembled people for whatever rewards and standings you could achieve. But it must be more complicated than just slapping a casino onto your usual M+.
I actually think it is cool 1 spec can cheese here and another spec can cheese there, but that is my oppinion. It becomes a problem when 1 spec can cheese everywhere and others nowhere.
They should just make an alternative ‘build your own group of NPCs’ mode for mythic plus so dps who can’t get into real keys have something to do.
I would be happier if they put resources into making tanking/healing more fun / better overall. But yeah. I don’t care if they implement your sort of thing, as long as it does not mess with regular m+. I would never touch it tough. Transitioning from DPS to tank is already challenging. I cannot even imagine trying to heal. Especially in fully automated queue.
Thing is, any game with real class diversity looks unbalanced from a distance. If a spell doesn’t look OP, then it’s weak.
If a game has enough depth, it will have room for each class to make use of its situational, “overpowered” abilities. So imo the solution isn’t more class homogenization but better encounter/dungeon design.
OK. Then lets do this though experiment: 3 dungeons and 2 healers.
These dungeons each has a mega dot that is super hard to heal through. Healer A) can dispell 1 dot (say diseases), healer B can dispell the other (say curses).
You would be in a world where healer A) can time the dungeon he can dispell ona +30 but healer B) can only do it on a +20. And vice versa. And the third dungeon with 2 boses, where 1 boss is curses and the other is deseases no healer can time that beyond a +20.
That is a massive problem. Imagine that RShamans were only taken for AD and nowhere else. And Priest only for DRH and nowhere else. It would be a nightmare!
Solution to the problem? Nerf the damage so much that ANY healer can spot heal the dot in case they dont have the dispell. But then its not a dispell mechanic anymore, its a healer check. So you loose the dispell fluff.
Dispell becomes trivial in that case. OR, alternatively if you insist on making that mechanic a dispell mechanic, then it should be “magic” category. Or dispellable by any healer.