I think that if we’re waiting for the project managers to go through these then we’ll definitely have way too many proposals for them to use their time wisely going through them. Ideally proposals would get moderated (like bug triage) for completeness and to look for spam.
After that I think it makes sense that people who can actually implement the proposal need to champion them. Rather than the project manager saying “hey team, I think this is a good idea” a developer says “hey, I like this idea and I’d like to work on it.” It could also allow volunteer developers to step up and say “I want to work on this, will it be well received?”
I also think we could take a page out of Participation’s strategy and start with a pilot. We need to not be afraid to iterate as new problems or good ideas come along.