Concerning FBReader's GUI. If the book selection is done outside FBReader,
Integrated FBReader 0.8.14 with ePub and Registry Support demonstrates that no GUI is required if you have 11 distinguishable key presses. I think
FBReader port to (Lbook|Hanlin) V3 works similarly.
If EFL can allow access to FBReader's GUI without a mouse/touchscreen that would be great. On an E-Ink screen, screen updates may be as much an issue as selection though. That is one reason why AdamB ditched FBReader's GUI on the iLiad, even though it has a touchscreen.