I think they might announce during the con. I wouldn't be surprised if it isn't just one, though. Probably Vivienne. They only did one last time and Sera/Dorian came out separately.
Aurgh, I really hope they announce both so we can all just know already.
If they announce only Vivienne, then poor people waiting for the guy option will go crazy. And if they announce the guy, then I will be the one who'll go crazy, wondering if Vivienne is an option at all (or straight).
Especially since she's the 'make it or break it' option for me. If she's bi, I'll be sad about Cass but we'll still get 3 lovely ladies who all seem interesting and amazing, and a nice diversity in appearance/personality. But if she isn't, that would mean gay ladies get less options and only one companion. And for me personally it'd mean getting my third and fourth choice out of 4 available ladies. So yh, I really hope they just tell us already XD