I too think that a custom web app is a great idea.
I think that one of the issues here is the format of RFCs - a text document is a more centralized format which worked great so far for Rust. However, as the community grows and we tackle bigger and more complex issues together as a community, i think the process becomes a joint brainstorming more than a single person’s idea/design.
Therefore, I think we need a graphical format such as a mind-map at least for the initial stages. the RFC text IMO is just the final stage - it is the proposed spec doc of the proposed final design and it could be extracted semi-automatically from the mind-map.