In my opinion, the biggest problems here is that github’s (and discourse’s) interface is not meant to be used for long conversations.
When commenting on an RFC, most people don’t read the entire conversation and bring up the same points that were already raised earlier in the conversation.
But how can you blame them when it’s so freaking long? For example I got interested in an RFC this morning, but the comments are 36 pages of text long! Either I read everything and it take me the whole morning, or I don’t read it and I’ll be “that guy” who brings up a point that was already discussed earlier. The end result is that I won’t participate in that discussion at all, even though I think I have an important point. I’ll wait until the RFC is approved, then if necessary raise my point in the tracking issue, which is usually less flooded.
The same problem arises if you open your own RFC. As you are supposed to defend your RFC, you are also logically supposed to read all the comments. But instead of reading few constructive comments, you get flooded by walls of text. I personally have two RFCs in mind that I’d like to propose, but that I won’t because of this point alone.
Compare this to reddit’s interface. Sometimes some RFCs have been linked on reddit and discussed on reddit, and it makes it pretty clear that their interface is much more readable for long discussions. Obviously I’m not saying that we should move the discussions to reddit, but I think it shows a clear problem.