I'm a relative newcomer too— started about two years ago with a Flake-only workflow on Nix 2.3. My sense in observing the debate over this time is that about 20% of the objections are technical in nature, while 80% are around governance— feeling that the feature was smuggled into the main repo as a prototype, despite there being existing external projects (niv) that were trying to accomplish a lot of the same things.