At the moment I can't say I'm loving the idea of so many of the characters from the other franchise in this one. Perhaps it will end up being great, which I hope it does, but it sounds more like a fourth film in the other X-Men series as opposed to the second in the First Class series. Perhaps they will do a good mix of it feeling like both but I want the focus to be on the First Class characters.
That's part of why I liked First Class so much. The fact it didn't have some of the actors from the other X-men films and focused on new characters.
I hated the casting of Halle Berry and Shawn Ashmore and found the portrayal of Rogue played by Anna Paquin to be annoying. So having all three invade the First Class sequel is a massive turn off for me.