the closed-source exporters proposal with donations could work
We have already thought about options like this in detail. Writing an exporter is a tiny fraction of the amount of work that goes in to the editor, so we'd be doing a monumental amount of work on the editor, only to sell exporters which are highly vulnerable to duplication by other open source projects or even third party commercial developers, so I really doubt that'd work at all in the long term.
We plan for the exporters to be open-source though - this should make it very easy for open-source devs to improve the runtime, or write an exporter for a platform of their choice (e.g. Linux), without impacting us. So parts of C2 will still be open source!