The thing the GPL requires is that I also provide it for free. Now, why would anyone buy a free thing? To support the devs. To encourage this sort of business model. To get a build that's known to be working and supported and not have to deal with the hassle of compiling things themselves.
Not sure why we should encourage using open source as a vehicle to market and get free work building your fundamentals. Just to reap the profits yourself later.
(In theory!)
Basically, the paid content will boil down to a single-player campaign.
The funds help us finish and release the game which still needs a lot of focused effort which is not something you can reliably sustained without commissioning some of that work.
The post below explains it in detail.
https://www.beyondallreason.info/news/beyond-all-reason-and-...