I think combination of JUCE/IntelliJ pricing and Unreal Engine model would be a sweet spot:

1) Personal License - free if <50k annual revenue

2) Startup License - keep current price (500usd/month) but

a) allow 1 month subscription commitment instead of paying 1 year upfront

b) when subscription not get extended you should still be allowed to distribute product that is not updated

c) if you payed for 1-2 years of subscriptions and cancelled subscription after 1-2+ year, you should be able to keep using the version of Qt the moment when you first signed for .

3) allow Startup to choose another licensing option. Instead of paying upfront licensing fee, just allow paying annually 5% of revenue from products that keep using Qt.