My couple cents:
- hobbyist license - free (+ pay what you want) for projects that will not generate any revenue (free games etc.) - watermark, splash
- indie license - free IDE, a reasonable flat fee for each exporter used for distribution of the game that generates revenue, premium plugins
- developer license - free IDE, source code access, plugin SDK, a flat fee for each exporter used for distribution of the game, premium plugins
Fees are per game release. I believe flat fees are better than royalties, since royalties are a pain to administrate. Moreover, the more successful the game is, the more traffic it would drive toward Construct 2.
Also, since there'd be a fee for each exporter, the developer would want to polish his game before releasing it. So less half-assed games out there on the market.
Did you notice premium plugins? Those would be plugins created by community members or anyone outside Scirra; they could release plugins for free (hobby license) or premium plans (meaning that they get a small share of profit if their plugin is included in a licensed game). This would be a good incentive for developers to release quality plugins; the better plugin, the more likely it is to be included in a game project, thus more likely to earn moolah.
Each game would have its own license key integrated, which would then be checked with the Scirra database for authenicity of the game.
Everyone would want to start with the hobby license, which would be free and allow them to release as many free projects as they want - as long as they don't make any revenue (from sales, advertising, paypal etc.)
Should they want to sell the game, they'd have to get the individual indie license key for the game. This key would then be assigned to the game; it would also serve as the unique identifier for the game (and its revisions/patches).
The developer license would come with everything a developer would need to extend Construct 2.
Just my modest 2 cents.