Xaphiosis
Harnessing it this way:
https://www.mobileread.com/forums/showthread.php?t=11280
Might bring better results. (unfortunately it didn't work for me (I was thining about writing an fb2 viewer) with the latest ebook library, probably because some interfaces have changed, program was just eating heaps of memory non-stop) As it's easier to debug stuff on a desktop...
Igorks mentioned somewhere that he's stopped developing it, due to the lack of interest from users. Maybe if you contact him in a polite way, he'll have a look what's wrong with the current version.
Sony's current UI is (somewhat) easily programmable (and obviously easily debuggable/fixable) using javascript. Compiled stuff is needed only for performance critical apps (viewers).
PS
There is another eink related linux project:
http://openinkpot.org/wiki/Hardware
Somebody has tried to port it to 505, but didn't manage it. Anyway it's a place to ask people eink/linux related questions.
PS
I have a version of PRS-600 firmware, that calls shell script on startup if reader is not connected to USB (to be able to unbrick it, if you've screwed something via custom script)
), in case you something like that. mount --bind from there works like a charm. If you "bind" stuff directly from /Data, it might have unpleasant side effects when modifying files, but copying file to /tmp or dict partition (there are about 10 mb's of free spaca afair) works perfectly.