> Common python libraries that make use of environmental variables

I didn't say environment variables weren't commonly used. I'm talking about the specific functionality this issue is about.

> Overriding setup scripts is hardly a trivial task. One has to completely recreate the activate script to achieve the desired behavior.

Not trivial, but not overly onerous either, e.g. just point to your own scripts subtree in the overridden method. Isn't your proposal to submit a different activate script?

> the functionality I am requesting already exists across all shells

I'm talking about the code to set, reset your custom environment variables - where is that already existent across all shells?

I'm not saying what you want is unreasonable - it's just putting it into the stdlib this way that I'm not sure about.