Didn't one of the Japanese YouTube things outright mock Sakuda for removing most of the DOA girls in Prism, though? This one, to be precise:
I'm doubtful Prism will end up influencing DOAXVV into adding more OCs at the expense of the cut girls.
Either way, the only time we can definitely say Lisa, or any cut girl for that matter, is not happening is if they shut down the game without ever including any of them, or at the very least announce there won't be any new updates like with Mario Kart Tour (and let's not forget, even Sakuta made it clear in two publications [Famitsu and I think 4Gamer] that they're highly wanted, and they still repeatedly ask in the polls whether they want mainline girls in the game. Heck, with the Steam version, they even specifically asked who specifically they wanted in [too bad they had a glitch with the answer, though, and not just for that question, for similar questions as well, and it took until AFTER the poll ended for them to answer]).
EDIT: Also, there's this article as well, which if anything indicates that Sakuta probably is aware of Western reception to DOAXVV by now (presumably also aware of the demand for cut girls being even larger than expected, and based on Famitsu and 4Gamer in two separate events, he at least knew they were a high demand in Japan):
Recent Dead or Alive Xtreme titles haven't been available outside of Japan and certain Asian countries, but demand for them is strong.
automaton-media.com
And correct me if I'm mistaken, but I don't think we had any actual ambiguous 18 year olds since... ever (Marie Rose was one of the starter girls, so she really doesn't count. And Kanna's explicitly over a millennium old, so she doesn't count either). Probably the closest might have been Lobelia, and even there, her being at least as tall as Fiona if not slightly taller in-game (and Fiona's taller than Marie Rose anyways, even if still on the small side) is a pretty big hint that she's indeed 18, even if flat bread. And Luna has a large enough breast size that she obviously is 18 even if short.