There's no problem with the subscription model. Let me explain.
1. A subscription model will ensure that the devs are getting a steady income to continue develop their product, provide support andmaybe even afford to hire some people to add some of the most requested features. Is this a bad thing?
2. They could have planned it differently by already planning for a C4 or C3.5, next year where people would have to pay again, but it's not good to keep and maintain too many products. So going with a subscription model for C3 will ensure that people people who are using it, are getting the latest updates, bug fixes, for some time onwards, so they can focus on C3, leave C2 behind them and only provide minor fixes and tweaks for older products.
3. It's not corporate greed, it's just a business strategy so that they can continue to provide a good product, and good support, and continue the development. Would you be happy if your boss told you he won't pay your salary next month because he already payed you once. Maybe some people has used C2 for years and years, but are still expecting support and bug fixes and features.
4. Although i think the subscription model would work very well, if they want to cater for a lot of different target groups. Maybe they could lower the price a bit later on for the core features (for hobbyists), and add optional packages for people wanting native exporters, mobile development, kongregate package, 3d editor, team oriented features, monetization package. I would happily pay and support yearly, for ALL they features I want, and I don't have to pay for the features I don't want or use, but If I'm a hobbyist maybe the core features is enough.
I don't mind paying for things i like and especially for support, as C2 clearly stand out as one of the best support I ever had. I've posted several bugs and feature requests, that got fixed in the next updates.