This approach was extremely effective because the messages where so damned annoying and scary for non-techno users.
This is not only the minimum work and most efficient solution (No need for startup scanning), it could also be extremely effective if you get a popup the first time each new Deprecated method is run, even if you disabled the popup for the last one. Very annoying. I would rather we annoy the hell out of the users of these modules than break them altogether.
The most effect Shareware force payment scheme I’ve ever seen was one where there was a 1 second delay on program startup that increased by 1 second every day or two. You thought you could live with it, but after a couple of weeks it drove you mad.