Turns out Terraria for Stadia will still be a thing. After what looked like it would never happen due to Re-Logic co-creator having their Google account locked, Terraria is now going through certification to release for Stadia.
Read the full article here: https://www.gamingonlinux.com/2021/02/terraria-for-google-stadia-is-surprisingly-back-on-and-going-through-certification