hey ash, I still think it'd make a huge difference, psychologically, that you called the first complete version 2.0, and set benchmarks for what you would call 3.0, 4.0 etc. Make them legitimate goals, but don't have set time limits. it's not like photoshop is a totally different program each time they increment.
It would be the exact same business model, except it could be phrased much more attractively:
When you purchase Construct 2, you get two years of free upgrades, so you're future proofed if Construct 3 rolls around during that time, you won't have to repurchase. Even better : new features of Construct 3, such as Android Export and iPhone export, and Directx11 and Stereoscopic 3d support for the windows runtime, will be released as they are completed, so you don't have to wait for a future release date to start using them. Any updates you have received in this way during those 2 years you get to keep, even if you don't purchase the next version.