There are a number of projects doing this today with dual-license models(Permissive/Commercial). I'm not a lawyer and have no idea if they hold up in court/can be enforced but it absolutely is a thing today.

https://opensource.stackexchange.com/questions/5599/any-succ...

It might exist but open-core model ( https://en.wikipedia.org/wiki/Open-core_model ) is much more commmn. I went through QT project licensing FAQ and I still don't see any situation when I would be forced to pay for commercial license when creating commercial software. Some SO answers suggest that complying with LGPL is harder on mobile OSes. Anyway - if you release something on open license, you can't really limit its use, no matter how your second license is constructed. That is probably why paid add-ons are so popular.

These are a little different. So these "dual licensed" products work like this:

You get a GPL version of the code, which is free and nobody can charge you for, ever.

If you want to use the software in a way that is not GPL compatible you can opt for the other, paid for, license.

This works in some cases, but in the case of Godot (assuming we were to do something like this) is the MIT license, which already gives you the rights to do whatever you want.

And even in the GPL case, if the other license terms became too odious you could simply switch to the GPL version, and not pay.

Here's an example:

https://github.com/SixLabors/ImageSharp/blob/main/LICENSE#L2...

https://news.ycombinator.com/item?id=33301518

Again, nothing stops someone from forking and maintaining.

Are you saying this is not legally enforceable? Because I am under the impression from my legal council it is. I can ask again to get more clarity.

This is specific to GPL-style licences. You would have to meet the terms of the GPL anyway (i.e. provide your modified source code under the same licence).

The commercial licence is just an additional option for companies willing to pay to not adhere to the GPL terms.

There are certainly cases where maintainers have started licensing _new_ versions of a project under different, non-open source terms (Terraform, ElasticSearch etc.). But you're free to continue using any code that was released under the old licence.

There are some badly written licences which make it ambiguous whether the licence can be revoked in future (e.g. Wizards of the Coast with the OGL), but I have rarely seen this raised as a concern in a software context.

(IANAL, this is not legal advice, etc.)