That’s great! Bigbluebutton is on the wishlist, just a matter of time I guess.
I think I really should have a closer look at Mattermost, seems they have a lot of interfaces to other apps.
https://docs.mattermost.com/guides/integration.html
Another possibility is Matrix Synapse. It has many integrations too but It’s work in progress.
Mattermost already is a base package.