Edit: For more context, the README says:
> If you are interested in working on the implementation for an "active" RFC, but cannot determine if someone else is already working on it, feel free to ask (e.g. by leaving a comment on the associated issue).
I went and checked out the issues and couldn't tell which ones were active. (I also don't plan on implementing an RFC, so no worries if this is something that should be apparent to someone more involved.)