Taking bets on the likelihood that Nemesis will not be available from Zana in 3.7.0

Incubation orbs let you guarantee that a certain type of loot will drop after killing a certain number of monsters, including ones that guarantee you specific types of uniques. And can be applied to gear individually. And apparently give better drops, according to Chris - “By deferring the item drop and making the player work for it, we get to drop a better item than we otherwise would. We’re very concerned about power creep.”* So what's to stop players from just adding the incubation mod for unique belts on all of their gear slots (at roughly the same time), almost killing the requisite number of mobs, then finishing the kill streak for all of them in a Nemesis zone, thereby guaranteeing 10 unique belt drops?

Easy! Just don't offer Nemesis in 3.7.0. There's not much loss to trying it anyway, since it's a pretty good bonus to have regardless. Same argument for other league-specific and highly valuable uniques.

*Source:- https://www.mmobomb.com/features/preview-five-armies-clash-path-exiles-next-expansion-legion/

Nemesis isn't a prereq to aquire headhunter anyway. There are so many ways to get it now.