Failure deploying containers from OS X

[brrrocking]

For example, with

nixops create -d vbox-contain nixops/examples/trivial-container-in-vbox.nix
nixops deploy -d vbox-contain
#..Build vbox machine..
machine> building initial configuration...
error: assertion failed at /nix/store/4han2qc1f181nw7f1bvf1an721xdb796-nixpkgs-16.03pre75806.77f8f35/nixpkgs/pkgs/os-specific/linux/kernel/generic.nix:31:1
(use ‘--show-trace’ to show detailed location information)
error: Command '['nix-build', '<nixpkgs/nixos>', '-A', 'system', '-I', 'nixos-config=/var/folders/lv/g1444dx54dz8q2tc2lk3vy8h0000gn/T/nixops-tmpgddZKk/machine-initial.nix', '-I', 'nixops=/nix/store/fiapphz7gkhiirm01f2bl8nzn6rd9350-nixops-1.3.1/share/nix/nixops']' returned non-zero exit status 1

I see that at an backends/containers.py an initial container config is built against builtins.currentSystem. I assume that's the cause of the error, or am I missing a trick somewhere?

I've created a fork and branch that could avoid this but I'd like to check I'm not doing something dumb before I submit a PR.

Thanks!