"Despite the closely matched performance between users on both platforms seen in our cross-play Test Weekend, we always want to ensure our Ranked experiences are as closely matched and competitive as possible."
More or less, don't expect the different platforms to commingle during any type of serious play. Over on Xbox Wire, Gears developer The Coalition's Liam Ashley writes that both console and PC players had "closely-matched results" in terms of average kill-to-death ratios, score and kills per-match based on their respective skill ratings.
With this experiment in the books, it wouldn't be surprising if we see cross-platform play happen in other games. After all, the gulf between aiming accuracy via mouse and keyboard on a PC versus a gamepad is a pretty high bar to overcome. Now it's been addressed in a way that seemingly Microsoft and fans are happy with.
Since that hurdle has been addressed, what's stopping Microsoft from opening up people playing Forza on a PC against pals on Xboxes? So long as it isn't ranked competition, there shouldn't be too much pushback.