> and support having multiple simultaneous versions of any Python library installed.

Installed. Not loaded.

The reason is to do away with virtual environments.

I just want to say `import numpy@2.3.x as np` in my code. If 2.3.2 is installed, it gets loaded as the singleton runtime library. If it's not installed, load the closest numpy available and print a warning to stderr. If a transient dependency in the runtime tree wants an incompatible numpy, tough luck, the best you get is a warning message on stderr.

You already have the A, B, C dependency resolution problem you describe today. And if it's not caught at the time of installing your dependencies, you see the failure at runtime.