I'm definately not interested in hosting a central one as I don't want to create a point of centralisation and I do host content. You wouldn't need an instance per repo but you'd need to use an instance that you or someone else is hosting and allowing your pubkey to write to.

What in suggested would just make pulling proposal commits marginly more efficient. Thinking about it, probably only if the commits where too big for events and you had to use an alternative like I just mentioned with blossom.