Tina had BETTER be in DOA6, especially after Shimbori and Tom Lee both implied that they created Diego partly reflect American sensibilities (that gives me bad vibes as to what's going to happen to Tina and Bass regarding their chances of appearing in DOA6, or apparent lack thereof. I mean, I though Tina and Bass represented American sensibilities, so why the heck are they acting like Diego just now is reflecting that?). Although personally, after what they did to the girls in DOA6 (Leifang especially), I'm really nervous about what they're going to do to Tina, Ayane, Honoka, and/or Rachel (aka the big four) regarding bust sizes. I'm definitely pretty sure Tina's going to be next in line regarding DOAXVV, though, especially after Leifang was unveiled and assuming they do them in cut order.
As far as DOAX3U and its chances, to be fair, DOA5+ didn't really make much money, yet that never stopped them from making DOA5U as a result. Heck, technically, DOA5 owes its very existence to DOAP, a port for DOAX2, and that only sold a million units.
Whatever the case, only way to find out what exactly is going to be done for DOAXVV at TGS is to see it when it comes. Only thing we know for sure is whatever it is must be important enough to have it be announced at TGS and not simply be announced/teased on Twitter or Famitsu.