Ubisoft is currently working on bringing cross-platform functionality to its PvP titles, as stated by CEO Yves Guillemot. He also mentioned that it's not just a dream anymore; it's a reality being worked on.
"Our goal is to put crossplay on all the PvP games we have, over time,". "That's well on the way." quoted (Gamesindustry.biz)
Yves Guillemot didn't confirm which PvP games were getting the support first, however, it's believed that For Honor and Rainbow Six Siege will be first to get cross-platform support. It's also worth mentioning that the "Smash Bros-Esque" fighter Brawlhalla currently supports cross-platform play.
On a side note, some players will express their disapproval for cross-platform support when competing with mouse and keyboard players. However, the recent released Call of Duty: Modern Warfare has shown that when cross-platform play is implemented correctly it can make for a fun and balanced game.