The model you proposed is a bad one. No new comer will buy C2. It is in it alpha stage right now, you really have no great games to show off the product. It is prone to having bugs with each new up date. I think you should go the Video Ad revenue route along with the closed exporter.
First of all C2 user should have to assign the program to their users account.
So you know if people have payed for the experter or not.
One C2 pogram installed on one pc per user.
For non paying users there should be no exporters at all instead,
Non paying users can could post there games on Scirra gaming site.
This would be like a youtube for games site.
You could put video ads commercial to play before the game start like the videos in youtube.
you could put up html5 code so people link up the game to their web site, or share links to social site like face book, twitter,etc just like youtube dose.
So as people play the game and rate them, you could make best of game page.
Then you could create construct 2 gaming app for google chrome app store where the best games will be featured.
By doing all this you will get more people interested in C2. The people who make game and the people who play then.
If let users decide that their are willing to pay for the exporters (individual ones, or bundle packs) They would have to do it under their user account.
This was you could make money while C2 is in development and when it is out of development.
Edit: ash I really want to know what you think of this idea.