I think you're vastly overestimating how many communities actually matter. At least 90% of communities will be ghost towns. It's just too early to tell right now because the platform is basically in its first week of existence. You're planning a solution to a problem that won't exist.
I get it, some of the first comments I made when I joined were about how to combine communities across multiple instances. As I've spent more time here, I've begun to understand that it's not actually a problem. The easy solution is to subscribe to the biggest community and/or one on your home instance.
Besides that, I don't see much of a difference between manually going through hundreds of communities to add the ones you want, or going through hundreds of communities on a pre made list to remove the ones you don't want.