Still a bit of a dick move, though.
I don't know if it's a dick move so much as a non-move. Nobody expected Microsoft to ever bend on the cross-platform issue, and when they suddenly did, Sony had no market research or plans or insight on the matter that they're suddenly the bad guy on. Plus, of course, as the market leader it's not in their better interest to make the move right now (and BTW, not only would cross-play be a plus for Xbox, it's also conceivably be helpful for Microsoft's Win10 gambit against Steam and other PC gaming providers.) It hurts us gamers, but it's probably the wise move to not jump into the fight until well equipped.
But also, on Sony's side, Microsoft doesn't seem to be saying
how to do cross-console or what it means that they're open to allowing it (what's the matchmaking like? will any party or friend features become available via either console's player database APIs? will XBL cross-play features between Xbox and PC also be open for use where compatible on PS4?), they're just saying, "go ahead, knock yourself out." (We actually know that the answer is "no" so far to some of those questions based on previous cross-play between PC/mobile and either console.) Rocket League's Psyonix has its own service solution in place, but they haven't exactly talked about what that would look like if it happened or what they could or could not use from the XBL toolkit in linking the consoles. PC-to-PS4 cross-play in Rocket League has complaints about restrictions (I assume PC-to-Xbox has the same simple-matching-only?), it generally sounds like PS4-to-Xbox would be similarly rudimentary. I worry that if the walls broke down, both companies would fall into a blame battle over who left the most shackles on. And gamers looking at this opening move from Microsoft as a doorway to cross-platform CoD or Overwatch might not be expecting what few doors they'll find open to them on the other side if even either console allows cross-play to go that far.