What I'm interested is rather something different.

Someone in our FC is playing on the PS3 and is wondering if it's possible to switch to the PC by just buying the PC version of the expansion.

So the question is this:
- Now: have only PS3 license.
- 3.0: want to play on the PC, ditch the PS3.
What must one do?
1. Just buy PC version of the expansion. No need to buy PS3 version of the expansion.
2. Must buy PC version and PS3 version of the expansion.