I don't know what "the method already allows for existing files" means.  Since the target directory can't exist, there can be no existing files.

In unix, this kind of capability is provided by a combination of shell globbing and 'cp -r', and by default it does replace existing files.  So it would be reasonable for exists_ok to mean exactly that: replace anything that currently exists, if it does.

I think that would be a reasonable API, but the implementation isn't as simple as just passing through the exists_ok flag to makedirs.

I do not think that *just* making it OK for the destination directory to exist would be a good API.