pruneaue [she/her]

You can totally use grub with boot.loader.grub

I dont really have enlightenment for you unfortunately.
As someone else pointed out, in terms of fork i think what there is out there currently is lix as an alternative to cppNix, and i think auxolotl is planning on replacing nixpkgs/nixos

While i get the concern and am not a fan of this myself. What youre asking for is a tall order. You could host a mirror yourself on an alternative that suits you (realistically there are probably already mirrors though i havent checked)