I worked on https://microco.sm with mattrco and it was forum/community software too. It looks like https://www.lfgss.com/

The #1 problem with a community startup: Every community is itself a startup.

The revenue math and compounded growth all makes sense, but you need to assume that few of your communities survive, and that they each take as long as a startup to get traction and grow.

If it takes you 1 year to get an MVP of sufficient quality to start attracting communities, it's still going to take the community at least a year to have sufficient attractiveness to bring in members. And it's unlikely that either will take as short as a year, and if it did that isn't going to be enough to bring in another round of funds to keep going.

Community startups are hard.