I have thought of a way that D4 can stay online only and give some of the players a way to play without ever seeing another player.
It would be to have two buttons that you can choose with each of your characters at anytime you want.
Hitting the private button would mean that you wouldn’t see anyone in town and there wouldn’t be a shared world where you would see other players. No PvP or anything that takes more than one player.
Hitting the multiplayer button would have all of what Blizz is wanting for D4. The shared world, world events, PvP and the rest.
This is the best of both worlds where Blizz still gets what it wants is an online only game. But still gives us the choice of playing entirely solo or playing with others.
I think this would be a win win for all.