I am one of the many that is furious about the exclusion of focus frame. I understand it was not openly aviable in vanilla, but it was used my MOST raiders (also in dugeons) by players knowing what they was doing. SO then it WAS indeed aviable as a function to use. I do plead (and i mean (PLEAD) to include it as a frame to enable/disable in settings. The purists shouldn’t have a say in this really (again as it was aviable to use as a script). Also one of the reasons this should be implented is for helping disabled people with easier focus ont he main tank when doing dung/raids. I am sadly one of those that have a consentration issue, and to keep targeting the tank between fights and the assist (or have to make assist macro every time a new tank change is a pain to me). It’s confusing enough to pay attention to the few macros for the fighting itself on mouse and actionbars alone. It is desired to again be able to rigthtclick the frame and set focus to the tank so we can use /assist focus in our macros and rotations. Please Blizzard, give us a choice to use or not use. Noone says the purist fanboys are forced to use it or something. Let us choose. Also remember that most players are by now used to focus. I don’t ask to include anything else in retail, but focus should be a part of the default frames as we used it since vanilla anyways. It is a stupid move to not include it, and can result in alot of players refusing to play classic just because of this IMPORTANT function.
I am not playing healer. That’s not a issue if I did have to watch the partyframes. What I am talking about is the constantly stresstest to always try to keep up with what mob tank is pulling. I noticed in classic it’s way more common that people attack different mobs. And that leads to wipes. Also as stated, for some of us playing (wow also have players with minor/more servere disabilities… Ex: Person with one hand using legal in game api for macros, and using follow on tank while mashing tank focus to fight, those players would be restricted to retail even if they want to play classic they cant do that the same way. So focus should been kept in classic even. Blizzard has already made sure to implent options for colorblind people (not sure if in classic, didn’t check, but I think so). I am aware that all gamecreators won’t take measures for this, but after all wow is the biggest game in the world, and they should let as many as possible be able to play it. Implenting a focusframe isn’t a big thing to ask to keep. It’s a more or less a function heavily used since long before first expansion even and has always been used. To be honest I am not doing instances, so I level classic only by doing questing. Thankfully I found a nice guild with mature people, so won’t be a rush and stressed pain to raid with them when the time comes. But everyone ain’t that lucky. Alltoghether I was able to keep up thanks to focus in retail, and I do consider to go back to the asocial environment if I feel to do serious stuff. Not sure I can in classic, at least I am gonna try Ps: I am aware I can use /assist, but thats beside the point. That’s what I gonna use with guild however as I will raid often with same people. Not as easy when playing with random folks and have to change macros each time tank changes .
A sidenote. Focus was intended to be in classic from the very start, it was just not visible as a frame until later when they decided it as a good thing to let us have, but by then the code was already ripped apart by the nerds and all serious players used it anyways (among other things that’s good they patched tought to be fair. Sadly they follow the majority of the fanboys and purist classic players. So doub’t we see it coming any time soon. Money is more important than serving the minority of paying customers. ALso since they are using the engine for WOTLK they should allow us to use frames and macros as it where in that game version. Maybe we can use something like /targetfriend /assist (with a class conditon or something), not sure if it can be done at all, else everyone would been using it by now probably.
I understand this is not set focus, however have you tried enabling Target of Target in Combat options? This will at least indicate which target your tank is on. I also do miss the set focus option, especially for pvp reasons, but i have no problems in pve - just make sure to have target of target enabled if you have not already.
But everyone ain’t that lucky. Alltoghether I was able to keep up thanks to focus in retail, and I do consider to go back to the asocial environment if I feel to do serious stuff. Not sure I can in classic, at least I am gonna try 
Ps: I am aware I can use /assist, but thats beside the point. That’s what I gonna use with guild however as I will raid often with same people. Not as easy when playing with random folks and have to change macros each time tank changes .