Just to grudges, I have with the mod. I really like the idea of giving the player the ability to speak, but having a single voice line is quite limiting. To solve this, you can of course add more voice lines to each character, but how when should different voice lines play?
I think it would be cool to make state-based voices, so that depending on your state you would you can say something different with a single button. So while player is waiting, sonic can yawn and Shadow can grunt.
Maybe it would be cool if you don't need to press a button at all to activate the voiceline, maybe doing some actions would have a chance to activate certain voicelines .
Also if you don't have enough similar voices to go around with, maybe the use of AI generated voices could come in handy, even though it could sound a bit janky.