I wonder if this concern could be partly alleviated through a price lock-in strategy. There could be a contract that says because the subscriber has paid for N months, that subscriber is eligible to keep paying the same price for 5-10 years, regardless of the price for other subscribers. This could incentivize people to start their subscription early.

That wouldn't stop the developer from abandoning the project though. I don't like using closed source tools when I can avoid it. Visual studio is a big exception because Microsoft will never abandon it in a million years, it's literally their flagship IDE.

The same argument can be made for the jet brains IDEs. But a closed source tool made by a solo developer just seems too risky for me, even if the OP was giving it away I'd be a little bit reluctant to use it.