Yeah, that's the scuttlebutt. There's sort of a tradition in Japanese politics where there's a rebellion like this, where you can't just cross the floor like in England. You have to set up a new party and then that party has to legally merge with the party you want to join. If Maehara was just a lone rebel, he'd have to spend time as an independent before he could join Ishin (if that is his desired aim, and it very well might be given how right wing he is, even though he's always been very anti-LDP, so he's spent most of his career as a member of center-left/liberal parties). But a large scale revolt like this has to be done in this roundabout way. It's just an odd conceit of Japanese politics. Of course, Maehara's imploded every single party he's joined, so Ishin might be very reluctant to bring him in, too.