Note that PEP 459 currently proposes preserving this capability as "python.commands.prebuilt", so I personally consider it reasonable as a way of packaging arbitrary executables and non-entry-point based scripts.
Yes, this will prove valuable (for other things than dlls, admittedly).
The main problem with using it for DLLs is the potential for "DLL hell" that you and others have mentioned, as version management on DLLs installed into shared directories can get very messy.
We control our environment and package only what is needed in it. This makes a micro system in which everything is controlled and isolated, even the global dlls (to the virtual env) I wanted to install. They become only accessible to the activated environment. I don’t see how it can become DLL hell in this situation.
But hearing many fine and useful comments on the thread made me change my mind and package the dependency near the extension module.
I still find that something like pep 459 will be really useful.
To the list: Thanks for all you input.