Just wanted to make a thread to confirm that Team 17 seem to be working on crossplatform and are estimating that it'll be ready by around the end of October. Here's the source:

http://steamcommunity.com/app/327030/discussions/0/343786746013559793/

To be 100% precise, that they are aiming for a system that will let Steam players link with GOG players, and will remove the current Linux / Mac / Windows split too.

Great news!

Hope this helps out anyone who may be considering a refund to make a more informed decision. :)