I'm not very keen on this approach, because it needs to be implemented across all shells and maintenance in this area can be a headache because not everyone has knowledge of multiple shells.

There already are hooks for customising behaviour - you can subclass EnvBuilder and override e.g. setup_scripts to update the venv with the exact scripts you want. This puts the maintenance cost onto the people who need this functionality (it doesn't seem like a very common use case).