I don't think PS4 versions of games will be gimped directly by devs, as some people are worrying. People are professional, they won't sabotage the title just to keep MS happy.
Rather, the "gimping" will be more indirect. I'm guessing for multiplatform games, that means whatever resolution, AA, framerate etc the developer can achieve on XB1 for a given game will likely be what they target for PS4. "Lets get the XB1 to this level, and we know the PS4 version will perform fine here".
I worry, that indirectly, the focus will be on getting the XB1 version of a game to a certain base performance metric, and less focus will go into taking advantage of what the PS4 could really do with it if it was the "lead" platform.
I don't know if I'm making sense. In short, no one is gonna sabotage their PS4 games out of fear of MS reprisal. I just think version of PS4 (multiplat) games will suffer, because the focus will be more about getting XB1 to a certain performance level, then just mimicking that on PS4.