This is great. Needs to find it's way into bundler. ;)
Bundler is a tool to manage which versions of which gems a project depends on – I don’t see how this API could go “into” Bundler. I think you mean that you want somebody to write a gem that provides a Ruby wrapper for this API.
Not sure I agree. There is a shorthand github option in bundler already which is there (presumably) due to the fact that a good percentage of the gems are sourced from there.
It would be helpful if pre-bundle update to know that the significant gem source is not available and exiting.