The only endgame pillar meant for real people and not professional gaming organizations, you mean.
Because m+ scales infinitely, there’s always a level of key harder than any boss in the mythic raid. Blizzard just had the good sense not to gate gear behind it.
Because that would be terrible, might drop m+ participation down to a 4-5 digit number. And who would want that?
Sanguine would be fine with a few small tweaks, removing instances where there’s little/no counterplay or that disproportionately affect the risk/reward tradeoff for certain pulls.