The fine folks behind Gutenprint accepted my patch to support the Canon Selphy ES series, but thanks to a boneheaded mistake on my part, what got committed didn't actually work. So there's a fixup patch pending.
The real fun, however, is the need to write a custom CUPS backend to properly spool data to the printer. I have a little helper app (es_print_assist.c) that batches the writes properly, but it dumbly waits instead of properly polling the printer for its status. CUPS is a lot more complicated to figure out than Gutenprint, so further progress will be much slower.
Meanwhile, Photo Organizer 2.35 is coming along nicely; I'm at the point where I have to decide whether to go into -rc stabilization now, and save the next round of invasive changes for 2.36, or go ahead and make one or more of those changes now.
In particular, I want to be able to have PO auto-generate full-resolution JPEGs from the source RAW images. On the surface this is straightforward, but I want to implement this properly, by genericizing the "generate a down-scaled image and apply this set of transforms to it" code. This way additional sizes would be trivially easy to add, as would some of the changes I have in mind to make watermarking much more useful. Progress has been slow, but I'm almost done getting the low-level bits in place.
Anyway. Tons of stuff to do, never enough time..