When it comes to the most groundbreaking achievement in the face of modern gaming, Psyonix is basically saying "Pbbbbt" in the face of the challenge. In an interview with Gamespot, Psyonix VP Jeremy Dunham says the tech is figured out, now it's on Microsoft and Sony to make it happen...
"Technologically everything works, we've got it figured out, just a little bit of time to get everything up and running. Right now, excitement is the best way to put it. We just want to get in there and make it happen. Elation is probably another word I would use. We're just excited."
He also went on to talk about how this union will be crucial in the longevity of many third party titles. I completely agree! How many times have you seen a game that you love to play die online due to "flavor of the week" status?! It happens to me literally all the time. With 3x the options our favorite would have a much longer lifespan online!
Of course Sony and Xbox have not reached an official deal as of yet, so nothing happens until they say so.