Since I have a license for PC, and a license for PS4. Am I gonna have to buy 2 copies of the expansion or 1 copy will serve both? Because currently my subscription lets me log into both systems.

So lets say I buy the PC version of the expansion and not PS4, I log into my PC, put on some exclusive expansion gear, then go to the expansion area and log out. Then turn on my PS4 and log in, what would happen?