That's fair. I take automatic backups of the sheet, such that if access to that is eventually lost I can republish via another method.

Discord is used for the simple reason that the current goal is to gain as much traction and participation as possible. The Rocketchat server I host, and the IRC channels I could have used would both acted as barriers of entry to a lot of possible participants.

Perhaps with time I can push for a migration to a solution I host. For the moment I'll stick with these tools, and plan for their failure as best I can.

I'd suggest matrix. It may be the closest you can currently come to something self hosted where most people with reading skills can figure out how to join.

There's certainly irony there, but then they're actually getting on with stuff rather than debating tooling. Discord and sheets are also both free - anything else is going to require an investment of money and time.