I'm not centralizing my group subscriptions on purpose, but it's a #NetworkEffect caused by the lack of distributed !Fedgroups hosting -- if I could create another group on my server with the same group name, and if my server then shared the load to distribute messages for the same people already subscribed to that group on other servers, I would have created a new group. It would make groups more resilient when particular server disappears; the remaining servers would just redistribute the load to host the group. If you see a !GNUsocial developer you can pass on this great suggestion :-)