another suggestion: maybe could be also useful (and possibly easier, too) to work on the port of the application KindlePDFViewer on Kobo platform.
In case you don't know it: despite its name, it's a complete reader application, not limited to PDF (using mupdf engine), but it can also handle DJVU (based on djvulibre), EPUB, MOBI, TXT, etc.. (all other formats supported by crreader engine).
It's open souce, written in C and lua (for the interface part). It includes a file manager and has several advanced features like: pdf zoom and pan, 2-column mode, pdf reflow, and many many other.
At the moment kindles with keyboard are supported, but a W.I.P. version that will be shortly released will include support for Kindle Paperwhite.
It's actively developed so in case of needs, you may ask support to the developers for help.
It makes use of framebuffer for the display, so I think it could be adapted to kobo platform.
For further info: