Prior to my purchasing a license I was thinking much of the same as the poster. I think Scirra should include in the store ability to have a project converted to an export for a fee. Perhaps even a portion of that going toward full license purchase.
Not to give something to the user as much as a way of adding to sales. I would loved to have seen an actual game made by me transferred to a specific platform to help me in making my decision to invest fully.
I do agree there seems to be no restrictions so this will make it legal I am not certain though why a user who owns a capx he cant use wants it modified. perhaps they are looking for an export of some sort.
Also think if this idea is to grow then Scirra in order to prevent this will have to restrict the way free edition saves it's files. This would lead to other problems but if people are going to work around the license purchase then Scirra would have to do something.