How many successful open source projects aren't substantially supported by people getting paid to do that work as their job? One of the big challenges for most open source projects is getting enough time to make substantial progress.

I think one of the challenges here is that the rules are meant to support a theme and the open nature means there's a lot of scut work building a viable system, testing, and balancing it. As we've seen with other ares like video games which combine the creativity of story telling with relatively high expectations for completeness, that's a pretty challenging combination to get volunteers to support. Companies which do invest the time and resources are going to have a natural conflict about sharing that with potential competitors since they need to make pay and it seems pretty easy to imagine a lot of the outcomes ending up like Elastic/Amazon disputes.