Looks like a very interesting project, but maybe there's some misunderstandings about the license; from the readme:
> x64dbg is licensed under GPLv3, which means you can freely distribute and/or modify the source of x64dbg, as long as you share your changes with us.
Should probably read: "... as long as you make genuine offer of providing the source code and changes to those you distribute your version of x64dbg to."
In practice it of course makes sense to upstream changes, but there's nothing in the gpl about that.
That's fine, and it is of course how many projects use the GPL in most cases in practice -- but as it reads in the readme, it sounds like the GPL doesn't [allow] someone to fork the project, port it to say, OS X, or arm - and sell the changed fork to a to a customer without giving the changes back upstream. The porter would have to offer sources to the customer, and the customer would be free to upstream the sources - but from the GPL, there's no legal compulsion to do so.
Anyway, I guess I would have reworded it somewhat, to make it more obvious that the source is under GPL, but that the project welcomes and encourages upstreaming changes. This opposed to the code being under a modified GPL.
> x64dbg is licensed under GPLv3, which means you can freely distribute and/or modify the source of x64dbg, as long as you share your changes with us.
Should probably read: "... as long as you make genuine offer of providing the source code and changes to those you distribute your version of x64dbg to."
In practice it of course makes sense to upstream changes, but there's nothing in the gpl about that.