Thanks Kurt, you're taking the bull by the horns, as we say in french.
Can gitlab keep things in sync automatically? I suppose not, but it's fairly easy that someone adds a commit hook to it, I do that with my personal github repo already..
Even if microsoft goes the bad way with github, this will be a very easy move out, for us as for any other project hosted there, remember the sourceforge suicide. Indeed something like QT being bought would be a bigger problem. But we would be together with a large part of the open source projects of the world, I guess an "openQT" fork would appear the same day and most of the non-corporate QT developers would migrate to it. OpenCasCade would be a much more annoying problem, but there also, they learned to not underestimate the community, their project was almost forked out of their control at some point (the PythonOCC/OCE glory days), the same could happen again. You cannot unlicence what has already been open-sourced.
If microsoft has regained any little bit of notion, they will be VERY careful. This will be interesting to watch, from an anthropological point of view