Wouldn't mind something along those lines myself. We already have the Doppleganger, so the model is there- making her a regular enemy instead of a rare one probably wouldn't be too difficult? She's actually not that hard, just drop her HP some maybe. The guy that's written most of the existing mods has already figured out how to change the shopkeeper, so making some recolors might not be too difficult?

Including the female models with ♥♥♥♥♥ in the sex scenes would be pretty difficult, from what I understand of the game's coding, nice as it would be. Swapping the Doppleganger model in for the PC? No idea how hard or easy- though swapping just the battle models might not be too hard? Wouldn't work for the sex scenes probably- or at least not without looking silly with the ♥♥♥♥ clipping through everything.