TTS with coqui xTTS is fun to run with a known voice (10sec wav file is enought). It requires some resources but far less than STT like faster-whisper. I think the main issue is not running them but integrate them with the OS/softwares.

David Revoy did some search on finding a cheap hardware to draw using opensource software: https://www.davidrevoy.com/article972/my-solution-for-mobile-digital-painting-on-gnu-linux