Though not a language feature per say, I would love if the language would take on the packaging ecosystem and deliver a ground up approach that isn't just a kludge on a kludge on a kludge.
If you use setuptools and place all your configuration declaratively in setup.cfg it is not that bad.
I've started using Docker for ensuring prod behaves the same as dev. Going from Mac dev to Linux prod would otherwise cause trouble.
Does your container expose ports or need volumes? Does it need gunicorn or uwsgi in front of it? What about system packages? None of those (except maybe the last one) are really in the scope of the package manager.