Well, let's do a couple of comments in this hidden thread.
As you've surely noticed, I've been pretty silent past months here.
I bought a Kindle 4 last November and since then I've surprised myself using it more and more than my beloved DR800. As a cheap and small device I carry it on without much care...
Anyway, some months ago I got root access in the kindle and started looking for viewers for other formats (fb2, epub, etc).
I found 2 "new" (not so new in fact) great programs/libs.
One is CoolReader , an evolution of FBReader (and much better), that has become the default fb2,epub,mobi reader on my desktop and android phone.
The other is mupdf , a very fast program/library, for pdf reading, not based on poppler.
Both also works for Windows and Linux.
This week I've successfully cross-compiled both programs for DR. Mupdf as Linux target and CoolReader with a wxGTK gui (btw, I've built a wxgtk-2.8.12 ipkg as well).
They are not useful as they need much integration with refresh, user interface and many other details.
I suppose I won't have enough time to properly make them work, but I'm writing this in case someone is interested.
A native gtk+ & mupdf -based pdf viewer should not take much time for a couple of C-experienced developers. Mupdf comes with sample viewers. In fact, if anyone wants to try, I could help.
CoolReader is another beast. It's written in C++ so it's behind my skills.
My imagined perfect viewer should be something like , an unique viewer based on mupdf and coolreader engine...