Well, if you feel like it, 5 NV stacks before doing a boss = guaranteed legendary 
Not like many ppl run bosses with 5 stacks anyways, hence the point.

Don't see any problem to this, it's actually feasible if only they had more legendaries to go around (I can count there are less than 100 in the game). It also alleviates the problem of overpriced legendaries in AH and also help cater to those who stay away from the AH

Just as an example, I farm bosses in Torchlight for mysterious items (mysterious items are almost equal as legendaries in D3, they are the highest quality item in the game). My stash is full of level 20+ mysterious items, which is only useful when I'm level 20-30 (give or take), afterwhich that gear has no use for me when I farm better gear in later acts. Take note that this is the final boss of act 1, killing him will drop mysterious items 100% of the time, and it's random. The point of this is to actually encourage players to farm a boss so that they can farm usable gear to allow them to progress through the next act and also provides impetus to keep replaying the game.

Mobs do drop mysterious items from time to time, so it's not that all pointless to clear entire dungeons for loot. I smashed a pot and a mysterious dropped, was a pleasant surprise

Kill boss = get reward (D2 formula)
Kill boss = get nothing good = browse AH (D3 formula)