That makes no sense for free version, so let's better make it "30-days trial" .
GameMaker has this kind of "free version" and no one is using it.
Unity has that kind of free version too, and a whole lot of people are using it, including me . The feature list for the free version is pretty extensive. There are only a handful of runtime features that you can't use in the free version, most notably shadows, occlusion culling, post-process effects, and the splash screen. You can still make a good game without any of those.
GameMaker's limitations on their free version are way too harsh. You can't rotate sprites or define your own trigger events. There's no networking.
When I suggested that certain features of C2 be left only for the paid version I was mainly speaking of the commercial license. But you could also do something like OpenGL shaders for desktop games. That's an example of a feature that would be nice to have, but not necessary for game development. You'd still be able to use core functionality of C2 without them. GameMaker on the other hand is gimping major features.
So yeah, the main purpose of buying C2 would be to get the commercial license, but if it came with a few little extras on top (customizable splash, shaders, etc.) then that's just extra incentive.
Oh, and I'm not saying that C2 should copy Unity's model 100%. They allow you to use their free version to make commercial games as long as your game makes less than $100,000. The free version of C2 could be strictly for non-commercial use. Which I think is totally fair, if you plan to make money off of it then the guys who made C2 should get a little something.
would it be a one off payment or would you have to pay for updates?
I don't think I know of any software companies that make you pay for updates.