Excellent idea, which resonates with my own proposal to maintain (and hopefully make more homogeneous) the twelve European hiking E-paths. The tags are similar, the problems are similar, and the tools are the same. Maybe we should coordinate the two working groups, or even combine them?
As for the medium, Iād say anything but email, please 
My own experience is that Telegram/Matrix, Discourse and the wiki each covers a different phase of the discussions, from unstructured short-lived brainstorming to formal proposals that can be tested.