While I appreciate the concept of new angle bracket syntax, I don’t think the Nix language needs flake-specific syntax. Flakes have been adopted by the majority of the community - but NIX_PATH was previously adopted by the majority of the community. The shortcomings of flakes are well-documented, and they are still experimental for established reasons. Even the biggest proponents of Flake stabilization acknowledge that future iterations on Flakes will happen, and plan on supporting them.
I don’t think entrenching ourselves further in flakeland is the right move. I’d prefer to see angle brackets used for something more meaningful, like providing a module system with faster evaluation.