Maybe it's not such a crazy idea as it sounds at first. We have Star Citizen, Elite Dangerous, and even Duke Nukem Forever got eventually released. WG4 is a bit of a community dream so the crowdfunding model might be suited.
Still I think you're maybe trying to solve the wrong problem. If Eugen wanted to make WG4 today, they'd be able to raise the money, with Steel Division not being a flop and probably another title being ready to be announced at some point and so. Is WG4 really the best opportunity that they should commit all their developers to?
The specifics can be tricky. Probably you wouldn't want to return money received, esp. if you already spent it. What kind of liability is there if you promise things and give control to backers - how to make everyone feel they got what they paid for? There could be brand risk with creative crowdfunding schemes. Why not just sell virtual spadochroniartze and T-80U for hundreds or thousands of bucks so you can view them in your hangar years before, like Star Citizen did - and got away with? Or maybe pump out DLC after DLC instead of all that crowdfunding trouble? After all Wing Commander and Bruce Roberts had more of a following than MadMat and WarGame.
Nerdfish wrote:What's the total market value of Eugen stocks ?
That's a bit of a tricky question. If a tree falls in the forest, how many wooden chairs hit the ground?
For companies not listed, you get anything like market value only if you approach them with the interest to buy and with convincing amounts of cash in hand. Or, if you somehow get their financial figures and other business information, you can make highly educated guesses. You can do some math yourself: games sold x sticker price of game x discount - what goes to Steam, Paradox, marketing, etc.