In a regular development/publishing scenario I don't think you could demand that they're keeping their promise, they can do whatever they want. But this was a crowd-funding project. They obviously need to keep their promise to those who funded the development. Someone who helped funding Project Cars because of the WiiU version and maybe even bought a WiiU because they knew PCars would arrive on it should obviously not sit there empty handed in the end. That would be absurd. They obviously need to refund those people, and it would probably be wise to put away the pitchforks because this is fresh news and maybe they're planning a refund as we speak. Or better yet, to get out of the bad light, they could send out a PS4/XB/PC with the game to them
Hehe not likely I know. But doing nothing at all, except saying sorry, is the worst thing they can do right now, it would put them in the same seat as Gearbox, and blaiming Nintendo for not launching new hardware doesn't help their situation one bit. They need to do it right, and do it now, not in 6 months, they need to do this right away before the bad mouthing gets out of hand and the wrong gaming press people who feed on others misery picks it up too.