If you were to save a document as a PDF from a MorphOS program, use VPDF to save it all as an image. e.g. jpg, at whatever resolution can be saved at, then copy the image(s) to a supported memory card for the Epson RX620 then use the Epson RX620 to print that from the memory card using it as a standalone printer/scanner/memory card image processing device - would that work sufficiently well for you with MorphOS? It's just an option to use it, though not as a connected printer though.

It would allow you to use it with MorphOS, but it would not have an actual printer driver, as Zukow has already said it uses a printer driver that he sadly cannot support with our current printing system. Nice printer/scanner/etc. though.