While I understand your need to find a proper business model to monetise your investment, I am a bit worried on the trend. I had a bad experience in the past with a security software tool initially marketed by a developer for a very reasonable price, then acquired by a large company, with the result of prices jumping over 500%.
I understand it’s not easy to keep a fees structure that doesn’t penalise existing users while at the same time ensuring any important developments are paid an extra fee. But I feel that if you call your licenses “perpetual”, there should be a minimum update version across releases, where clients don’t need to pay anything extra for keeping the same level of functionality.
This would mean only charging serious enhancements/modules. Just my 2 cents.