Gutenprint 5.2.11-pre1 was released this weekend. It contains the usual support for a pile of new printers, and improvements for many previously-supported models. I'll only speak about stuff I had a hand in:
First, the newly-supported models that are reported to be working quite well:
- Canon SELPHY CP820 and CP910
- Citizen CW-01 / Olmec OP900
- DNP DS620/DS620A
- Mitsubishi CP-3800DW
Next, new models that were added but have received no testing:
- Sony UP-CR10L (aka DNP SL10)
- Shinko S1245 
Models that have much-improved support:
- DNP DS40/DS80/RX1 
- Citizen CX/CX-W/CY 
- Canon SELPHY CP900
- Kodak 605, 6800, and 6850 
- Mitsubishi CP9550 family (including the CP9550DW-S!)
- Sony UP-DR200
Finally, models that are improved or added, but will require much more work before they are considered useful:
- Mitsubishi CP-D70/D707/K60/D80 
- Ciaat Brava 21 
- Kodak 305 
- Kodak 8810
- Shinko S6145 
- Shinko S6245
 The Shinko S1245 is notable in that I've already completed a full-featured backend that just needs testing with a real printer.
 These models are all related, and use an unknown color scaling/dithering algorithm that must be reverse-engineered before the printers become usable.
 The Kodak 68x0 family in particular is considerably more robust in the face of errors, media mismatches, and status reporting.
 The DNP/Citizen backend was greatly improved, and is far, far more robust than it used to be. Error detection and recovery, general buffer management, handling media/print job mismatches, and even general status queries were all improved.
Oh, just to forestall the question, all printers with multi-cut modes (eg 2x6 strips) have full support, but will require a minor patch to be applied to Gutenprint before compiling.
I'll end this with my usual request for testers, especially ones with access to the Shinko S1245, Sony UP-CR10L, and DNP SL10 models since the work is already completed. As for what's next, the Shinko S6245 is the most promising candidate.
Thanks go out to everyone who has helped -- be it testing or providing USB dumps; sending over documentation (Yay, Shinko!), or actual printers (Yay, LiveLink!). There are others I would like to acknowledge but they have asked to remain anonymous. Thank you, all.