Then why a 50% drop rate from bosses and only after 5 NV stacks? And listing bosses that drop them? If you only need them once, that is completely irrelevant and the drops would annoy everyone after the first week. With that drop rate. Especially since you can just buy them.
Something is odd, I have a feeling you need the recipe each time you want to craft. Otherwise the drop rates and the requirements and the exclusion of end bosses don't make any sense
The new crafting recipes are not consumed on use, no.
We wanted them to be on bosses so players have a more "targeted" location to farm for the recipes, similar to the way that the Infernal Machine recipe worked (but obviously not exactly the same). We also chose the bosses we did specifically, as they are generally less farmed than others.
As for why a 50% drop rate? It's a problem of competing goals:
1. Add something to the game to act as gold sink
2. Add something to the game that's thematically interesting
In order to achieve 1, whatever we add needs to widely available. In order to achieve 2, we can't just distribute those additions solely through vendors.
We'd also rather have a situation where the recipes are selling for vendor cost on the Auction House rather than one where only a few people have access to them (and their respective items). We'll see how things go on the PTR. We also wouldn't be opposed to reducing the drop rates over time if that's what's best for the health of the game.