I 100% support properly done open-world NMs, with item-based pops being my favorite.

Put the items as a very rare drop on ALL mobs, or all mobs in a specific ZONE, or a specific DUNGEON. Take the item, gather your friends, pop the NM, get some cool loot/crafting items/etc.

Lottery pops are also cool. As are timed pops, just don't make the timers too ridiculous, maybe every few hours. The whole "zomg call everyone to log on ASAP because a 7 day spawn is up" experience is something that should've died back in the 90s. Everything doesn't have to be instanced, but we should be able to dedicate a reasonable amount of time to going out and hunting an NM or two with our LS and actually, y'know, see an NM or two.