Can I make one suggestion? Why not try and base ALL of the i/o between the exercise and the server on SCORM 2004? That way, your module will support ANY SCORM content that complies with the standard; for special types of content that you care about, and which perhaps don't use SCORM 2004 (such as HotPot 6 exercises, which use SCORM 1.2), you could provide a translation layer. From what I've seen on the SCORM module forum, SCORM 2004 support is still fairly rudimentary; you could join forces with those developers.
I hope you do find a way to bring in a revenue stream. We know from our own experience that Hot Potatoes would have ceased to exist three or four years ago without the revenue that comes from licences.