Still not possible to play concurrently.

Maybe you can't play the same game (I haven't tried) but it is definitely possible to let your kid play other games. I have this very setup with my son and it works. An other advantage to this setup is that you can select which of your games to let your kid play.

Maybe they changed something very recently, but it was certainly impossible to play two games before without offline shenanigans.

I don't know, we've been doing it for years. Maybe it's a regional thing? One account for me and one for my kid. I authorize the use of my games for his account on his machine (I need to login with my account on his machine to authorize his machine, I did it just the other day as the machine authorization only seems to last for a while). Then he can install and play any game of mine I allow (or all) once he logs back in with his account.