I'd just like to share that, while I was trying to set up my printer, I found out that the current version (3.13.3) of the HPLIP plugin was compiled only for x86 architecture and, thus, it doesn't work for our beloved Raspberry Pi.
BUT merlin has started a bug report to ask for an ARM support in their plugin. You can check it in the following url: https://bugs.launchpad.net/hplip/+bug/1152219
The more people voting as affected, the better!