At first I thought this was a good idea, but now I'm not sure. Instead of encouraging the need for that sort of manual work to group every similar community for every topic, I think we should let the communities naturally converge on the winning community.
Okay, but I see no reason to intentionally make that issue worse.
I'm not saying those spaces can't be used. Ideally each instance would end up with its own set of popular communities that have become the one true community. But it's a much better user experience if every instance doesn't have all of the communities from every other instance duplicated.
Because if I subscribe to all of them, sometimes I will see 100 identical posts of the relevant news. And if I subscribe to just one, then I'm missing out on a lot of content.