The Cult of the Dead Cow started working on mesh networks back in the 90s.  Ain't heard much from them of late, but they were smart people.  Maybe they got it working and that's why I don't hear much...  

A big issue is the security cores on chips commercially manufactured and available.  Not much point in software based security if the hardware has built in back doors.  Eventually, we'll be able to print our own chips, and that will allow a real solution.