I don't think we've really done this sort of PR / discussion via GitHub before. Usually we'd use the forum or better yet IRC when the right people are online. I'd be curious to see what other projects do, give Google a spin! :-)

As for PR vs forum I'd say bigger individual changes in a forum thread (since it is sort of "one" topic, which works) and "shotgun" blast questions like these proably better via PR :D

Either way yeah can close a question-only PR early just so it doesn't get merged, or just put a disclaimer at the top. Easy :-)

Good point on the forum/wiki bits, we still lack quite a bit of that. Poking at a forum thread on that would be another great way to help! Lest we forget the good ideas in this rather temporal PR.