The crux of it all is that we don't want artists to be off on their own saying "this is what we want, now do it" since it creates an us vs them kind of situation and is inflexible to the realities of what's possible, and what people are actually willing to code. It would be much better in a more inclusive situation where people can work and discuss things together. Not to mention the thought of trying to manage a beaurocratic structure like artists -> 'BUIG' -> FuBo -> coders mailing lists -> coders gives me shivers down my spine

I think just having a functionality board which is pretty similat to what you were mentioning in that step A, with strict limits forbidding technical discussions - keeping the focus to Blender and its use would be best. The FuBo isn't proposed be in the "coders' domain" - it's supposed to be separate from technical development discussions, yet including ideas from all people.
Having a one way process like you described would also take away a major purpose of a FuBo (or whatever you want to call it) - that is a resource for coders to help figure out how to implement their ideas and new features. It will be helpful for such a group to be used as a research resource that coders can bounce ideas off for how new features can fit into blender. This is what I mean about a two-way process and working together. Artists certainly don't have a monopoly on new feature ideas, and neither do coders. It's also pointless just submitting feature requests, if nobody wants to code them. That's why we need more collaboration in a kind of 'reserved space' where users don't have to get caught up in the technical stuff, just discuss the functionality.