There's a lot here I'd not considered so this is helpful, thanks.
The splintering is an issue I've run into already. When I searched for squaredcircle on the assumption the subreddit community had started moving, I got results for five 'squaredcircle' communities across five different instances and none of them have a significant membership. I don't want to further splinter the community by creating another community as you say, so I figured I'd just have to subscribe to all of them and wait to see which one takes off. I guess it's going to be down to the subreddit mods to say "this is where we're going", if that's even what they want to do. Until then it might be a bit daunting for those making the jump but it is what it is.