The Luminai are a race unto themselves, so I think it's highly unlikely that there will be any playable ones. They're supposed to be highly secretive, rarely making public appearances, so I'd say it's all but confirmed that there won't be any among the "generic" Cassians. Since highborn Cassians have only trace amounts of Eldan blood, there's nothing there to suggest that their breeding practices are as rigorous as the Luminai's. Yes, they probably strive for purity, but that still leaves them open to the rest of the aristocracy. I'd imagine that arranged marriages are common among highborn Cassians, but I can't see anyone but the Luminai resorting to the more drastic methods of enforced blood purity. The lowborn Cassians are exempt from any of this because they have no discernable Eldan blood whatsoever.