The priority of the binary cache info file is currently hardcoded to 30 https://github.com/edolstra/nix-serve/blob/master/nix-serve.psgi#L18, it would be nice to have an option to change this value, i.e. using a command-line parameter.

This would be especially useful when running multiple binary caches. I personally run 3 binary caches, one on my vserver, one at home and one at the local hackerspace. It would be nice to have nixos automatically chose the caches in the local network, which setting the priority would facilitate.