Okay, so I guess I was wrong about additional printer hacking. Despite the 12-hour days at the office over the past few weeks (we got our first silicon back, and software is the ring that binds everything together in the darkness), I'm still spending time writing code when I get home.
First, I added support for the Sony UP-CR10L and its rebadged brethren, the DNP SL10. I've had these on my to-do list for a while; I'd already decoded everything and updated the existing UP-DR150/200 backend to handle the new bits, but never got around to adding proper support into Gutenprint. That's now done, and once I get the USB PIDs, it should JustWork(tm).
Beyond that, I've knocked out a few things on the bug list. One I just fixed affected pipelined printing on the DNP/Citizen printers, and it was most easily triggered by multi-page print jobs. With Gutenprint 5.2.10's backend, the printer would just abort the job after the first page, but if you were using a development snapshot after 2014-06-04, it would automatically retry the job, resulting in an endless printing of page 1 over and over again.
The bug was due to the backend mistakenly treating the "Printing, with one available buffer for a 300dpi or small 600dpi job" status as an error.
At least folks won't have to wait for the next Gutenprint release to pick up the latest backend code.
I have a rather large photo backlog from the past month to sort through. That will be my weekend project..