This is a good watershed moment for FOSS as a whole and I hope Mozilla decide to fork Mattermost or something similar and expand it to suit their needs over using Slack if that's the direction they head.

Something federated and encrypted like Matrix/Riot would be fun. Having something that's federated would be lovely to see other members of the FOSS community start to come together over time.

but there is a lot of problems with those rich text/react/Electron thick apps can be "painful" tho