Start with the Clara as a base and modify/add.
Battery life like earlier readers (like the Kobo Glo HD). Minimum of 8GB of storage. Minimum of 1GB of memory. Add water proofing (like many of the newer readers, no door). A Plastic substrate (like the Forma). Bluetooth for external device page turns (I believe that there are readers that can do this). Easily replaceable battery (I believe early readers had replaceable batteries.) Faster performance without sacrificing battery life (or very little battery life). Configurable tap areas (I believe koreader has this). Lighter weight <= 180g.
Ability to patch (and someone who will do the patches
). I include this because I like that Kobo has more formatting (gradations in font size, line spacing, margins), but I would like more gradations then the current firmware. Or, Kobo's configuration file, but merge in Kindle's FONT_RAMP (and if we can add functionality, more/add ramp choices, and make ramps for line spacing and margins).
And if I count apps as ereaders, more configuration options like Stanza.
And if we can modify existing hardware/firmware... haptic touch all around the front bezzle ( like the Voyage's buttons), but with user configurable areas.