Yeah it's a shame it took so long. I myself had this plan for a long time, but never got around to set it in action, because I thought it was too hard. But with @mastohost it's really, really easy.
For now I won't allow individuals to sign up and I do have some feelers out to some groups. As soon as some groups have joined we'll decide if we want to open up the instance for individuals too.
Alternatively I could also create another instance for individuals as a sub-domain.
This is an official mastodon instance for activist groups of the global climate justice movement.