Yeah, even before this I honestly didn't expect him to show up again in the pages of Sideways. I expected it, and still do, in Snyder's event. That title, and specifically the writers involved, just sparked the opportunity to revive him.
"They can be a great people Kal-El, they wish to be. They only lack the light to show the way. For this reason above all, their capacity for good, I have sent them you. My only son." - Jor-El
Yeah, I don't think the intent was ever for New 52 Superman to become exclusively part of Sideways supporting cast. The idea was simply to reintroduce a pure, unaltered version of what Morrison originally created and set him loose on the Multiverse so future creators could use him whenever they wanted without having to worry about how he fit into the mainline DCU Earth's continuity.
I'm rereading the earlier New 52 Superman stories. It saddens me to see so many great ideas and concepts that will never appear again because people at DC are too cowards to stick to their guns.
"Longtime fans will read the book and bitch about it NO MATTER WHAT."
- Grant Morrison
As if.
Sideways would have to return, or anyone liking the New version of Superman (and Wonder Woman, to me. The two are made stronger together). And DC current slate of writers shares at least apathy toward this period, and they know fans prefer to eat whatever Rebirth (and isn't Bendis) offered than even the best of The New 52 Superman - which is a shame.
We're stuck with Champions of the Privileged and Unjust Social Order forever now.
Didio seems to be the only person who has any interest in him as a character so unless he gets another book (he runs the place so I suppose it's possible) I doubt we'll see him again. And even then Didio would have to put him in the book which there's no guarantee of that either. That Sideways issue may have just been a last send off.
Assassinate Putin!
I'll preface this with the fact that the current downsizing at DC makes pretty much all of this moot. I don't think we see any new lines outside of Wonder Comics and whatever the Walmart thing is turning into.
That said, Sideways doesn't have to return for this Superman to return. That was just the method chosen to get him out there. He's out in the multiverse now. Anywhere any writer might want him to be. Any question of if he could ever be seen again doesn't hinge on whether or not we see Sideways again at all.
But for the above reasons, the chances of this if there were ever any just got a whole lot slimmer, unfortunately.
"They can be a great people Kal-El, they wish to be. They only lack the light to show the way. For this reason above all, their capacity for good, I have sent them you. My only son." - Jor-El
Wonder Comics would be a good imprint to use for him actually.
I think Morrison implied this is the New52 Superman but didn't confirm it given the whole Superman Reborn fiasco.