See this interesting post on using nix with bazel:
https://www.tweag.io/posts/2018-03-15-bazel-nix.htmlnix is a reproducible package manager. We have been investigating using nix for python packages. There is support for building even some of the harder packages to build with nix. It looks like we could use rules_nix to possibly solve the problem of building external deps.
I think we should investigate if we can possibly leap ahead by leveraging all this existing work.