Different versions of Poser have had no problem running at the same time on the same machine before. I have had Poser 7, 8, and 9 running at the same time on my Mac, and I have had Poser 11 and Poser 2014 running at the same time on my current Windows PC. Unless something changes, I see no reason why Posers 11 and 12 won't run at the same time on the same machine.