I have two comments and a question.
First, my comment is that GitHub claims the right to use any public code on the Internet, not just GitHub. This means that they claim the right to mine code on Sourcehut, or in my case, on my personal Gitea instance. I'm not sure your suggestion 1 covers that. I think it should.
Second, users could fork code from Sourcehut onto GitHub, and then even if GitHub only uses code on GitHub, they could then use that code. This is, of course, a consequence of using DVCS's and can't be worked around. Your first suggestion should also address this, in my opinion, by allowing original authors to opt-out.
Third, my question: you've surely seen the licenses I have been developing against Copilot ([1]) since you've emailed me about them. Do you think the way I've approached the anti-Copilot clause is still free and open? For reference, this is the clause in all of my licenses:
> In this license, the phrase “this software” includes the source code licensed under this license. It also includes the output of any execution of any algorithm that uses all or part of this software as all or part of its input, but only if the output itself is software.
(The rest of the license then says it applies to "this software.")