Hi @dfisher,
as a read-across I would like to mention that the concept of a NNS treasury was also recently raised in the context of the Community fund (CF) in this post.
In particular the post also mentions that the NNS treasury is meant to be extendable to use cases beyond the CF
As you point out, there is a lot of design work (and risks) we will have to deal with it.
Nevertheless, also from my perspective, creating a NNS treasury is worthwhile pursuing.