It is ambiguous when you say that it is not going to fly. It may mean “You can always ask, but nobody will do the change.” which is probable, whilst the fact that it would not work is false.
For the users having to structure their code, it is only if they need to handle such interfacing problems. So nothing is taken away from users, they don’t loose anything. They just have new solutions: for all dependencies conflicts below, they have a simple solution, for dependencies conflicts in their own code, they have a way to handle it through boilerplate code. It brings solutions to the table, previously they had none other than looking for other packages as dependencies or recode part of a dependency. Nothing is perfect, nothing is free of some burden, nothing justifies that on Internet the majority of persons that react are nay-sayers.
A solution with a performance penalty *notable only when it is used* is always better than no solution. Your argument is a classical fake argument of nay-sayers and doesn’t imply that they always do very optimized code. Moreover, when the Python interpreter resolves an import it must load the function tokens and their adresses to use them afterward; resolving two imports for two distinct versions of the same library would prepare similarly what is needed to use some adress when some function token is parsed without conflicting because of the distinct contexts (or the distinct tokens in the user code), I see no reason that the interpreter would be slowed down apart of the additional tokens to keep in memory; the penalty for the performance and memory would be measured; it would be mainly on the import mechanism that it could be slowed down very slightly in my opinion, and once the import is done, I see no reason for a substantial penalty. If you think otherwise, please explain your reasoning.
Fine, when you say that, you perfectly know that the entry cost on a project like Python is high, and that almost nobody has the time to understand the internals of a project like Python just to make a proof of concept and experience further bashing afterwards. I’m already struggling to redo most of my own Free Software work because of sabotage. Weeks or months of work that vanishes in thin air. I’m always struggling because of crackers and intelligence services and I don’t know who mess with my code to enshittify my life. If I take now two weeks of work to make a proof of concept, I am almost certain that they will not let me succeed or find a way to screw another of my projects during the time. I don’t have yet taken the decision to do or not a proof of concept but you don’t imagine how mad I am against people that steal the life of others and nobody helps.