Is there a possibility of adding a TTS feature for a sort of pet or custom Item? Was thinking It'd be cool to have an item grow like a face or something when triggered by TTS.

Most likely not unfortunately. It'd be way beyond the scope of vTuber kit at this point. But I'm sure there are other options out there that you can use alongside vTuber Kit for a similar effect! You can possibly look into something like VTSPog