My quest for a reliable and acceptably powerful personal all-in-one printer is apparently over. See updates
I bought an Epson WorkForce WF-3620 networked inkjet printer/scanner/copier for 90 CAD.
Debian Jessie contains Epson's printer-driver-escpr 1.4.1, which supports that printer. But the CUPS test page I printed was incredibly pale. Upgrading to unstable's version of the driver (1.6.3) was easy, but the pages printed still had way too little ink, even though the cartridges were full (although pages were readable).
The workaround is in the end most simple. The default Media Type is, unsurprisingly, "plain papers-Standard". But surprisingly, that type gives abnormally pale pages. Changing that to either "plain papers-Standard-Vivid" or "plain papers-High" solves the problem. Both seem equally readable. The latter seems to print more slowly.
Except for a doubtful label in the Web interface (printing statistics are in a page named "Maintenance"), and a worthless sticker meant to make the printer French (they visibly sent the wrong model), everything but the drivers has been working fine so far. It has USB, Ethernet and 802.11 connectivity, another USB port for scanning to a USB drive, 4 ink cartridges, an automated document feeder, a web interface, a color touchscreen, actual buttons and more. Quite an upgrade over my last Epson (Stylus COLOR 200)
This could still be easily improved. The interface does not say that the ink level of cartridges is fine. It would also be useful to detail printing statistics further, for example by indicating the number of pages requested from each client IP address. And of course at what time cartridges were last replaced.
Update 1: cartridge replacement is deficient. Once you find how to initiate it, the instructions are wrong (no, you do not open the scanner to change the cartridges).
Update 2: Copying works most of the time, but has crashed the printer once (requires hard reboot - i.e. unplugging the power cord).
Update 3: The UI for print head alignment is ridiculously unclear.
Update 4: 23 months after purchase, black print quality suddenly dropped dramatically, making the printer essentially unusable for printing black. 200 CAD and many man-hours spent on cartridge replacement, manual print head cleaning, automatic print head cleaning and multiple alignments only worsened the situation. I have replaced the WF-3620.