Regarding these issues, the only one that would be problematic moving to gitea would be pages. Everything else works pretty easily with gitea. Not saying this is reason enough to make a swap, simply that it isn’t an insurmountable hurdle by any stretch.
mirror the organization repos on both github/gitlab and you still get search index 
To me it is an issue of power. Power is consolidated to a few tech giants. Microsoft is making lots of moves on the AI front, and of course we all know how companies like Google and Amazon violate human’s right to privacy. As plutocratic governments merge with tech giants, humans are greatly in danger of slipping in to a deeply problematic Orwellian survellience state. I think any conversations about redistributing power is worth having. The principle may be more important than the convenience of using the super shiny low maintenance tools provided by these giants
Mostly just project organization and management features. Maybe it is a non-issue. I think setting up gitfoss.org as a non profit could be a good move to prevent it from turning in to something designed to benefit corporations and the wealthy.
I would be happy to migrate all the issues in to github or somewhere else. Probably a script we could set up to use API keys and automate the movement of the stuff. Then close out issues that are non-important.
Ultimately, I am not sure the best solutions for anything. Just proposing ideas, I see all of your points as valid and making a lot of sense.
Ultimately, I want to build things to make your life easier so the project can move faster. I personally believe that issue tracking and project boards are very important. Of course we could simply leverage what github already has to offer, but ultimately having some sort of framework where people can jump in and contribute valuable things is important IMO.
Maybe I am too focused on the color of the bikeshed. But I want more people to be able use and contribute to our our bikeshed. That is a big upside of CI and automated testing IMO. Currently it seems like in many ways you are the person who helps make sure nothing breaks. In some ways, you are a dependency (I do not mean this offensively btw. It is a compliment to the great thing you have built ). But I want to reduce the reliance on you as a dependency so things can grow reliably for many years to come.
Again, maybe I am overthinking all of it, and I should just build more things and not worry about it.
