Locked screen, chose "New Session", got a "Switch To" button for my user which upon clicking dropped me back into my existing session.
A difficulty we have is that when the session goes away, the login screen doesn't update because we never reload() the model - this is also true for the "Switch Session" button on the lock screen which only appears if tehre's another session. Is this something that is likely? Maybe somehow we could call reload() whenever the login screen gets switched to? I didn't test what happens if I actually log out from my session, ie. whether SDDM comes up after that or my session si still there for a brief moment which causes it to continue showing the "Switch To".
{F355086}
On one hand I'd like to have that in 5.8 (minus the "Switch To" we could just keep "Login" without the password field I support) as that's "how it should have been" but on the other hand this is a quite stark behavior change for a patch release.