AFAIK, affected versions never made it to stable as there was no reason to backport it.
xz is necessarily in the stdenv. Patching it means rebuilding the world, no matter what you optimise.
That's not what flakes are important for at all.
Though unless you already know what flakes could do for you, I agree, you don't need to even think about flakes. They only concern one specific aspect of Nix and aren't even the only solution to that problem.
It's working on my end.
Is "Grouped Results" disabled in settings?
They have attempted to make this but you have to be rather specific to trigger local results. "Chinese takeaway" will not trigger it for instance but "Chinese takeaway near me" will.
Improving this is hard but a possibility I see would be to have certain categories of search default to region-local (as in: country, general region) or location-specifc (town, borough).
Searches on the topic of shopping, taxes, bureaucracy etc. should automatically make results local.
Searches on the topic of restaurants, shops, leasure, transport etc. should be location-specific.
Determining these topics would be the hard part though; especially given that it'd have to happen in multiple languages.
Certainly better than the U.S. in that regard but I wouldn't consider Germany "resilient" either.
Sorry, can't answer that as my crystal ball is broken at the moment.
I think it could be because Google may offer them quite a bit longer hardware support. They had to go with some industrial SoC for the FP5 to get Qualcomm to offer even a half decent hardware support cycle.
This has nothing to do with "unstable" or the specific channel. It could have happened on the stable channel too; depending on the timing.