It has always been about the N900 form factor and OS. I would love to do another hardware generation jump and maybe bump back to N800 form factor so we get more LCD area.
Throw a Maemo5 like GUI FOSS Gnu-Linux OS onto it with an APK loading environment and we would have something great and ready for everyday use.
While wishing I also want a pocsag pager module installed so I can leave the cellular modem powered down and can still take incoming pages and callback quickly while operating radio-silent and untracked by corporate and government busybodies.
Internal power, charging, and maybe a strip of GPIOs and serial as well as USB host pads would enable plugging or soldering down striped down USB dongles or other hardware for easy custom aftermarket expansion, similar to the hackerbuss designed for the N900.