I believe when Kain absorbed Raziel into the Reaver at the end of Defiance he was cured of the corruption brought on by Nupraptor going insane, I had always assumed that healed the Pillar of Balance and would allow the Pillars to be restored. This would also reseal the Hylden in the other dimension they were banished to. It's been a while so I can't say for sure that's what happened, but I remember it happening something like that. Also, when do the Hylden possess the one true vampire? I don't remember that happening.

The main thing I want to know is, are they going to get back as many of the original voice cast as possible? I have some reservations about another game being made after so long and by a different team of people. But, if they get the original voice cast, that would do a lot to assuage my fears, and show they actually care about the original material. Here's hoping.