I’ve never used Elm, but that’s not how reasonable open source projects work. Red Hat maintains several rather divergent forks of Linux and they’re still in the club. I personally run a fork of Linux that I maintain, and I’m in the club. The only people who attract serious ire from the club are people who distribute out-of-tree modules that play poorly with the rest of the system. Even in that case, no one gets excommunicated, but the upstream kernel makes no particular effort to keep problematic modules working.