So I've been mulling it over, and I honestly think there can only be one Clark Kent aka Kal-el aka Superman. Doesn't completely matter where he's from but there shouldn't be two or more of him at one time, in my opinion.
To expound on that a little more, I mean if the two or more "Clarks" have negligible differences at best, then I think there is no point. In fact, at that point it's my sincere belief that the two characters begin cutting into the others character progression and possible story points. What comes to mind, for me, is Supergirl and Power girl. They'd been in the same universe for quite some time, and for the most part Power girl had been the far more constant and memorable character using the "Supergirl" idea, but since she wasn't Supergirl proper she was a bit of a black sheep in the family. Her book was allowed to progress the character because going backwards would mean her being Supergirl, but that also seemed to me going forward for Supergirl would be Power girl. In my opinion Supergirl just sort of ended up being, at best, a mediocre character pre-52.
If at some point the plan is to have both Clarks present on Earth then you've got a very similar situation where one of these Clarks will be a rather mediocre character because of the ceiling shaped like him. The stuff that makes Clark interesting and compelling is the progression and wide shot look of his life. You put both these characters on Earth and we may very well have a situation where New 52 Clark is basically frozen in time and personality just for the sake of setting himself apart from the older Clark. A perpetually overly hot tempered and less mature Superman who is less likely to progress as a person.
This doesn't leave Superdad unscathed either, mind you. Far from it. You've got a Superman who is perpetually a stick in the mud and overly authoritative. You see what I'm getting at? It's like deliberately trying to turn them into parodies of their worst critiques from us the fans. The best case will be that one luckily gets the lion's share of the fans via and writer with an interesting vision for the character.
The solution to this seems simple, right? "Get Superdad outta here then". Well we're about to have a pretty extended run of the Rebirth era, and what that translates to is time with the character and his family for us the fans to grow attachments to. If that's not enough Jon and Damian will likely be building a pretty great bond in what Didio has proclaimed his favorite book of the bunch. You simply can't just shuck them off world after that. "Get rid of Clark and Lois but keep Jon then". Not a smart idea. Jon's point as a character is then taken away. His point is in relation to his family and their dynamic together. You take that away and you're basically left with the safe uncomfortable "we're related but not related" ideas present in Superboy Kon-el. It's a waste of a perfectly good character(s).
What it's basically come down to in my mind is that we have three options for optimum success given the stage set. Option 1. You drum up some story about maybe how the universe has taken notice of their being two Clark Kents and Lois Lanes, and now it need to rectify this. So somehow we get a story where the Supermen have to graft together their lives in order to save everything or whatever. When it's all said and done no one remembers.
Option 2. Soft reboot (no way in hell they're getting rid of Snyder's Batman run) that keeps the Lois, Clark, and Jon aspects. Play catch up using back ups and one shots that build a tapestry of this new guys life
Optional 3rd option would be the permanent death of the new 52 Superman and a soft reboot correction for Superdad.
You see, non of this would be an issue if the two Superman we super distinct. If it were say Hernan Guerra (Gods and Monsters), Val-Zod, President Superman, Captain Atom, or Superdoomsday. The list goes on. But what we have are two Supermen who were technically the same person at the start of New 52.
What does everyone else think?