This is the beginning of Phase 1 of my Rebirth mod plans. After studying the new Rebirth models, materials, and textures, I couldn't figure out a way to bring them to Remake as the differences were too significant. There's many more materials and texture slots which the current Remake modding tools don't allow for adding new materials, but I figured out a way to rearrange the new textures without losing any detail quality.
The differences are a bit subtle during gameplay, but it's very noticeable during cutscenes so far that I have seen.
With this mod set, I'll also be able to go back and revise my other Tifa Remake mods with the Rebirth model and textures as a base. There's still a bit a bug squashing I need to do before releasing this mod, but progress should be smooth from here and I should have this ready soon!
As for Phase 2 for Rebirth mods, it seems only texture replacements are still only possible, with static models being possible by a few modders that created the Remake modding tools, but no tools are available as of current.