My wishlist; feel free to start on some of these yourself:

• fix master with nix 2.3; it works with nix 2.2.2: example (I had to downgrade that Hydra builder for now)

• investigate avoiding the impurity from the builder's nix version. It just makes debugging the failures harder, e.g. now people (with nix >= 2.3) will be getting different errors than the Hydra job.

• investigate getting better error outputs from the job. IIRC now isn't an exception when you see

  parse error: Invalid numeric literal at line 1, column 6

  without a good hint of what's wrong (at least what file is referred to).