Not much. I've encountered a handful of esoteric file conversion tools, though I couldn't say whether any of those are still for sale/available now that you can

Not much. I've encountered a handful of esoteric file conversion tools, though I couldn't say whether any of those are still for sale/available now that you can hide the secret sauce behind a web front end. It doesn't seem impossible in principle, but anything viable has to be better than any open source tools that might be out there but also able to command an audience with enough money and inclination to pay for it despite whatever level of license infringement takes place. It sounds like quite a narrow scope!