[everforward]

> I's basically a big fuck you to anyone who does not commercializes his software but wants to contribute to the software ecosystem and only expects users to also contribute back to it.

The problem here is that "user contributions" are basically impossible to value. Who knows what they might have contributed, and what value others may be able to derive from those contributions. I can't think of a single good way to translate that into dollars. You could charge engineer hours, but who knows how many they would have contributed.

> Maybe we need a GPL4 with a building nuke. "You agree to pay 1 Trillion dollars if you do not publish your changes".

I hope this is in jest, because I fear something like that would chase off open source developers.

I do think it could use a penalties clause. I would suggest something in the net revenue or profit category. It makes the penalty scale, including scaling down to 0 for other open source projects. I don't want to encourage open source projects ignoring licenses, but I do think suing them for money seems unfair when the currency of open source is really contributions.

[mannerheim]

> You could charge engineer hours, but who knows how many they would have contributed.

I would guess courts have ways of determining this, perhaps via subject matter experts. It's not like GPL software is the only kind of software for which it might be impossible to obtain a proprietary license - there are probably many cases of proprietary software copying from other proprietary software, where one party isn't willing or able to provide a license to another (for instance, a company might be competing in the same space as another that copied their code, so they're unwilling to provide a license). But more likely a settlement would be reached in a case of clearcut copyright infringement.