Right now because it find the first importable name on the python path, and syntax doesn't give you any control over anything else than name, you can only install one version of something.
This means you cannot opt in to install 2 versions of the same lib for the sake of compat. Well, you can, but you have to vendor it manually, which is a lot of work.
NodeJS is the opposite, it will always let you install as many versions of any deps as sub deps request so you end up with 2000 times the same lib.