I just set up an account at fedia.io, which is an mbin instance. When I ran the script posted over here to copy my subscriptions I had 111 subscriptions succeed and 49 fail. I've been checking the ones that failed and they've all been ones that haven't had anyone post in them for 5 months or more, so I'm guessing those are "dead" anyway. Seems not too bad, I'll see how it goes I guess.
I posted this same response from both of my accounts, I'm going to watch to see how well it federates back and forth.