Did you even look at the affixes for Mythic+? Rotating affixes every week are going to do exactly what you described, they shouldn't feel ad nauseum at all. Changing the physical environments isn't really challenging after the first time you've done them. It's not just damage multipliers, some of the affixes are going to force you to run the dungeon in a certain way else face failing.
For example, Teeming/Skittish is going to increase the number of trash mobs in the instance, and cause the Tank to generate a lot less threat. This is going to force DPS players to play much more AOE oriented while focusing on personal survivability due to the lack of threat.
The next week, Raging/Necrotic is going to cause mobs to enrage at low health that deals damage and reduces the healing on a target. This means that trash packs have to die FAST, and an emphasis is going to play heavily on rotating defensive cooldowns to keep the Tank alive. DPS might have to help the healer heal the tank.
The next week, Bolstering/Decay is going to force your group to survive long trash battles, as the trash mobs buff each other on death while your group takes constant damage throughout the dungeon. Focus on survivability as much as possible.
Thank fuck there isn't Skittish/Necrotic because that would just be brutal.
I think, within the confines of what is interesting in the context of WoW, I can't really think of anything better myself. They can always add new affixes that dramatically alter the way you play the dungeon that aren't simply stat increases.
For example, what if they added an affix that caused enemies to run away when they reached low health? You'd need to really have your CC game on point or else they are going to pull another track pack on top of your ass.
Or an affix that made everyone completely immune to CC? Good luck.