FWIW, I think some form of #2 is inevitable if we really want design discussions to scale. Maybe we don’t quite need it yet, and we should certainly try all “type-1” solutions first so we keep type-2 solutions/barriers to a minimum, but I can’t see us never needing a barrier of some kind. But I don’t think that barriers to commenting necessarily mean leaving people unsatisfied.
The key thing is to distinguish between “comments” that everyone is effectively required to read before participating in the discussion at all, and “comments” that are optional to read or respond to. I think we can all agree that there should always be an official place (covered by the CoC, team members watching, etc) where anyone can comment on any RFC with no barrier other than the ability to write English. But we don’t need to make all of those comments automatically go in the “you must read this before commenting” pile the way github RFC threads implicitly do today.
For example (this is a strawman just to make my thoughts concrete enough to avoid misunderstanding the general idea, don’t worry about the details), we could lock comments on the github RFC pull request thread to just team members and facilitators because it’s their job to summarize discussion and ultimately accept/reject the RFC. Then have this or some other Discourse instance be the official place where anyone can post opinions, comments or questions related to the RFC, including disagreeing with past summaries, and it’d naturally be just as well-threaded as irlo is today (which is to say, not perfectly, but still asymptotically better than smushing everyone into one thread).
In addition to the many obvious threading benefits that every suggestion here hopes for, I like to think something like this would lead to more people participating, not less, because you no longer have to worry about your comment or question potentially wasting everyone’s time (it’d certainly have that effect on me), and you’d have far fewer “mandatory comments” to read before participating.