I think Mozilla could round up various offerings that would require little overhead to offer (similar to reselling Mullvad as Mozilla VPN). To round up a few:
Team Chat (resell EMS, Element Matrix Services, as Mozilla already uses Matrix and their team would likely be very friendly to a partnership similar to Mullvad): https://element.io/pricing
Personally I think a white-label e-mail solution would make sense, both for individuals and teams. For example mailbox.org's model is pretty good I think (not an ad, I am a paying customer).
I don't think that those solutions are something they can maintain, they did in the past Firefox Hello integrated in the browser that was a chat with videocamera support like 10 years ago...
About Mozilla Hubs I still don't know how many people use it right now every month...
I use — as probably you do — a pasword manager (pwms) outside Firefox. In order to get this workng with a browser, plugins and configuration are needed. Still the build in password and forms manager gets in the way.
I would love to see an industry standard across browsers that allows interoperability accross pwms. The idea being that any pwms can be registered in browser settings and will replace the in-browser vault and stores passwords in whatever pwms is used.