I completely agree. Some rotation is good.
The current system does not provide much rotation though. Virtually every week the same 2-3 dungeons give the best rewards per unit of difficulty, and the only thing that’s going to change that is if Blizzard manually goes in and changes the encounters, and since every dungeon is infinitely repeatable, you can keep running the same dungeon forever by just constantly finding new groups, which damages group cohesion and causes problems for the competitive side of the game. As such, M+ is at odds with itself - it tries to be a competitive system but does not reward being competitive.
My suggestion would cause some slightly longer-term rotation. In essence, about every month or so, 2 dungeons would fade out of relevance, and 2 would enter relevance. Sometimes quests and extra bosses and hidden hardmodes would pull you back into things you had put behind you, with timewalking certainly being a good candidate for this design.
It’s great that you enjoy M+, but might I suggest that you’re enjoying M+ because of the strength of the dungeons and not because of M+ as a system in and of itself?
Anybody here who actually enjoy how keystones work? Or are you like me - enjoying having hard dungeons, and just thinking of keystones as the way the game happens to deliver that?