The default careers are a great spread, in my humble opinion. The additional xenos races in Into The Storm (Orks and Kroot) and now in the upcoming Soul Reaver (Dark Eldar) add a lot to the game, and I think that the lack of Craftworlders isn't going to change. Want do you guys want to see next?
I'm hoping for an alternative to the Rogue Trader would be great, some kind of alternate owner of the vessel. A non-Astropath psyker could also be excellent. Some flavour of Astartes would be pandering, but fun. As for xenos, I would personally kill to see a Sslyth Mercenary (great warriors, loyal, very alien) or a Stryxis Nomad (surprising party faces, good plot hooks, under-utilized.) I'm also a sucker for Dark Eldar, and hope they get a small mountain of alternate ranks. Rak'Gol might be a distant stretch.
That's what you think.