I’d like to point out that if the Flakes project had been started by most other persons, it would have been a community/third party project instead of something part of code Nix. There would be no “upstream” in the way we are talking about here. And as @Ericson2314 already pointed out, we’d be probably better off that way as a whole. (Of course it is too late now, Flakes have picked up too much momentum too fundamentally change course)
A lot of peoples’ frustration with Flakes comes from the fact that they have been developed in a way which would be more appropriate for an external project to Nix than something weaved into its core functionality. This impedance mismatch has proven difficult to resolve and is an ongoing cause for tension, as clearly visible in this thread.
I can totally understand why people would like to see these issues resolved in upstream Nix instead. But I’d argue that moving some of that development out into external projects first, small experiments which can iterate at a faster pace, may actually be a good thing.