I'd like to see Miss Monday and Yaiba Kamikaze join the roster in DOA6 especially Miss Monday. I mean if Momiji and Rachel can join the fun why not them?
Rachel is the main female of Ninja Gaiden which is hailed by many as one of the best games of all time. People thought those two may be added as DLC in the Ultimate days, but Yaiba has been unheard of for a few years, and if they are only adding 1 new male and one 1 new female to start I would rather have completely new characters.
Though I would definitely choose Miss Monday over a Venus Vacation girl.