That sounds very nice. But you wouldn't normally put pylint into the standard requirements, would you, so you would have a dedicated, separate requirement file for it, to use with these services?
I often see a requirements.txt (with runtime dependencies) and a requirements-dev.txt (with test runners, linters, etc.) in projects.
So I went with that approach, which requires.io also supported out of the box, very nice.
I personally like to go even further and have one requirements file for every job on Travis (i.e. tests/pylint/flake8/...): https://github.com/qutebrowser/qutebrowser/tree/master/misc/requirements
Yes, sparing resources for them by specializing totally makes sense. I only have one job, but for all Python versions there, and I think I should have one dedicated for Travis, so I can add "redbaron" to development without making Travis download stuff not needed by it. These files can include one another as I have seen, so no duplication needed.
Anyway, thanks for the input. I had read of these things, but never realized I should have the issue myself.