For a while my company was considering docker precisely to keep an old python app (described as python 1.5) running. The dependencies of that app haven't been maintained in a decade, will never be upgraded and will likely disappear soon as the hosts remove their mercurial repos. Having the base machine running something modern with the old python stuff in a docker image seemed like a promising solution but the stuck with RHEL7 instead.
Thankfully it's no longer my problem.