I think if an item reward would be implemented, it should only be from a random spawned NM for the final battle ~ sometimes an NM spawns, sometimes its just a unique mob. And of course make them have a huge list of various items and drop %'s, so you won't always get what you want, just like when killing NMs...

Or another idea, when this NM should spawn and its defeated, everyone in the PT gets a token for that camp, {Camp Horizon Token} that can only be used at that camp. Then add a new token vendor in each camp that sells various pieces of gear to a set and other random goodies, and you'll have to participate in behest from multiple camps and NM battles, collecting tokens {as each item will have a token cost} to earn/purchase every piece. In the end, it'll make more players participate in behest all over the game instead of in select locations as it is now.