At that point, you're basically selling a freemium subscription, which is very hard to pull off properly for desktop software, and requires walking a very fine line: if too much of your functionality is paywalled, then the "free" version is useless and the whole exercise is pointless; but if too little of the functionality is paywalled, nobody will pay for your software. IDEs are a great example, because there is little functionality that is important enough to make users want to purchase a subscription, yet doesn't render the software redundant when a user stops paying and it's disabled. But I'd imagine there are also plenty of niches (like yours) for which this type of business model works incredibly well.

I hope it works out for you!