This is why I really liked the approach of using a github username as a namespace for rubygems, it lets you publish things but with some indication that it may just be for personal use.
Yeah the useful thing is namespaces, I agree it would be good to not tie it to any given platform. I remember the cargo (rust) folks discussed including some way to have a namespace. I don't remember the details but I was disappointed they decided not to go that route.
You can install directly from GitHub, bitbucket, etc. with pip, BTW. My point was that if I want to have packages for private use installable over the internet with package management tools for various languages, I have to put them on the public internet, or jump through some hoops.
Package management tools for both Rust and Go and JS do support direct github urls with minimal boilerplate. You have no reason to make something public unless you want to.
Using pip, and possibly other tools, you can try using a .netrc[0] file to manage login credentials for private repositories.
Although it is a cleartext file (so you may need to manage access to it, for instance when using it in CI), at least your credentials will not show up in log files.
