I'd love to see this continued for other Aliens like the Bith, Aqualish, Wookies, Selkath, and more. Of course, this is a really well made mod and looks very good. Definitely gonna use this for my playthroughs of kotor 1!
I haven't tested it in-game, but looking at the preview screenshot I think you should be able to plug the neck gap at least.
Edit: Yeah looking at the models and the texture, I think I see what the issue is there. You're relying on Blending Additive and setting the mesh alpha to 1.0 in the supermodel.
Edit 2: Edited version using the same technique as in my mod: