Always better to do the design doc up front IMO. It isn't clear to me what the boundaries are of what you're building. What about topN queries (i.e. ORDER BY and LIMIT clause)? It seems that this is only a partial solution that handles the simple "scan-only-no-post-processing" queries. Is that of value to folks?

Regarding a "hand off", who are you proposing handing it off to? This definitely needs a volunteer to own it if we want to get it to the point where it can be committed.