If there is no directory that accepts a content type, but the content type needs a directory, the user needs a warning that they need to create a directory that accepts the type first.
I'd actully say no to this. There is a use case for page types of directory entries to be made that arn't assigned to directory channels themselves (hidden entries). This could be:
Unpublished entires that have not yet been assigned any channels (enry is usually added first).
Child directory entries, which is something BHCC and I think others are now experimenting with, which would mean we want an entry but not have it in any listing, you have to go through anoher entry to get to it.
If there is no directory that accepts a content type, but the content type needs a directory, the user needs a warning that they need to create a directory that accepts the type first.