Hi Pual,
Thanks a lot for offering the help!
The koreader-base is quite stable right now, so I cannot think of any simple fix that's left over. But, yeah, feel free to send us PR if you find any bug in koreader-base.
If you would like help with the reader, there are two todos that haven't been added to the issue tracker yet. 1. dig through crengine's code and wrap it's dictionary support in cre module. 2. bring gettext to koreader-base so we can localize koreader.
We have lots of todos in the frontend part though. If you don't feel like coding in Lua, improving the user/dev document will also be very helpful. All the documents are in the wiki.
Xephyr with dithering looks cool to me too
no need to have pressure, just pick anything and hack for fun.