After exploring the demo files a bit more, from what I can tell so far, all males use the same body base mesh/textures and all females also use the same body base mesh/textures. So it should be somewhat straight forward to mod other characters outfits onto each other. Such as Azucena's bikini outfit onto Asuka like this example.
The customization features, on the other hand, aren't as in-depth as I initially thought they would be, but I still I think it should be interesting to try modding the customization outfits as well. As it would be a very unintrusive way to apply these mods.
I've seen a few mods start being released for Tekken 8, but I have yet to find a tutorial walking through the steps to reinject the the modded files back into the game. But I will continue to keep my eye out for them, and if you guys see any modding guides out there feel free to let me know as well!