This is the part I absolutely don't get about this. Plus windows create a better visual boundary for the context-switch tab groups are supposed to be as you minimize one and restore another.

Why not just use windows? 🤷 I sure hope they keep the implementation of this simple and end up just doing that for the user. Create new tab group -> color-coded new window opens up, gently nudging the user towards how simple the solution to their problem actually is.