Discourse now has an ActivityPub plugin, which allows federation, both with other Discourse instances (like community.openfl.org and community.heaps.io, as long as they also enable this plugin) and with applications such as Mastodon. This would allow me and others to conveniently watch this forum from more places and jump in to answer questions people post. They have some good videos on how to set this up. In particular, the sharing of rooms looks like it would helpful to me.
I’m not sure what kind of setup you have in mind.
I wouldn’t want posts from those communities to end up here for example. And most posts here wouldn’t make much sense in other communities (except announcements maybe?)
I think there’s a distinction though — ActivityPub doesn’t necessarily mean everything floods in both directions. You could follow the forum elsewhere to read and reply without the feed of announcements going out to Mastodon or other servers. Could be worth asking the Discourse devs exactly how the plugin handles one-way follows.