In MoP they added personal loot to the raids so items won’t be able to be sold anymore, maybe they will do paid runs or something like that I guess, but that doesn’t guarantee an item.
Probably there will be paid runs like you mention. In won’t matter if the loot is not guaranteed. It’s not now either. You need the loot to drop first and then bid on it.
You don’t need to pay in GDKPs unless the item you want drops. That will probably make paid runs less popular overall.
GDKPs won’t die just because of personal loot.
Why? Because you can change from personal loot to master loot.
I don’t recall Pandaria being first expansion that introduced personal loot, but personal loot didn’t replace group loot nor did it replace master loot (just because most players use personal loot, doesn’t mean you can’t use other loot systems)
No they did not. If anything personal like was added it was in LFR only. As the matter of fact even WoD had master loot, the system only got flexible that you could kill a boss a week with as many groups as you wanted, but was eligible for their loot only once. Imagine how many GDKP runs could a pumper make on one character only changing the master looter and buyers. Oh wait… No one is going to play WoD anyway again.