I think the big thing is that in setting up the backstory for Arena, they were insistent that the exact details of the Nephilim stuff *not* be revealed -- that suggest, to me, that it's a potential playground for a future story (I certainly wouldn't count on seeing Casey again, soon... and definately not Steven Petraca).
You know what? I actually think I'd be fine with not seeing Casey again.
I have nothing against Prophecy or anything, but, for whatever reason, I was just never "sold" on Casey and his friends. Don't know why, but I just never felt as attached to them as I did the original characters.
That said, I know Chris Roberts has a 'prequel' concept that he'd like to develop given the right conditions...
A Chris Roberts involved WC prequel would definitely be cool, assuming he'd be willing to stop working on movies long enough to do it.
Any idea if the prequel he's interested in developing would deal with the start of the war with the Kilrathi? Or, would it focus more on the Pilgrim war?