OK, how about the 3.x series introduces tiered force pop NMS.
there are 12 tier 1 NM which lead to 6 tier 2 NM which lead to 3 tier 3 NM which lead to 1 tier 4 NM. each tier is progressively harder than the previous.
Each tier 1 NM is preceded by a need of two pop items which can be obtained from a quest or mob farm (if done by quest there can be a lock out of X hours/days/week before accepting again) or have it go through the leve system where you spend x amount of leves to pop a tier 1 NM.
After defeating a tier 1 NM they drop loot and 1 of two pop items to force pop a tier 2 NM. defeating a tier 2 drops loot, and 1 of 2 items to pop a t3, the T3 drops more loot and 1 of 3 items to pop the mega boss which drops the best loot.
so it's a pyramid
4
/ | \
3 3 3
/ \ / \ / \
2 2 2 2 2 2
/\ /\ /\ /\ /\ /\
11 11 11 11 11 11
Have this system set up in several zones.
Or have 8 man dungeons with hard trash pulls, which need to be off tanked or CC'd with slows, binds, sleeps, which leads to boss fights which have more than dodge mechanics, I would love to see some utility skills actually be put to some use. the whole dungeon culminates in a hard boss fight, not dictated by an enrage timer.
Make encounters challenging, but not DPS racing a clock. I'm sick of it.