It is live!

[Rannie]

There was definitely some previous information (though I only heard it second-hand without a source) that NG+ would let you wind back to earlier expansions but not Shadowbringers.

I assume we'll be level-unsynched during normal gameplay, but we really need to be synched for solo duties. They're generally meant to have an epic "story event" feel to them, and that would be lost if you had to play them at your current level and everything dies in one hit - whether you want it to or not.

Imagine one shotting zenos during the in crimson it began quest and then seeing your character knocked flat on their ass >.<