Unfortunately Mozilla seems having problems with managing larger products or changes. I was following recent (last year iirc) transition of Thunderbird from xul based extensions to webextensions - no updated roadmap, the new extension model was pushed to production while being only part ready. Examples provided by Mozilla team were outdated and some used features that were no longer available. Other features were not implemented, some worked for pop3 and not for imap accounts. This thing was and probably still is a mess.
So while the product you described seems to have some potential, i can't imagine it being run by Mozilla and attracting developers.