My 'bandar' essay considered this option as more cost effective than a low orbit radar/imint/elint equipped sat solution. I tied the main aspects of ISR into a single airship platform (akin to the E-10 concept) with remote datalink & comms connectivity to allow for unmanned operations and to promote a degree of persistence. There are obvious performance limitations to overcome but unmanned and pushed up high enough to avoid any gnd based threat has some merit IMHO.
That said though, I didn't win! So I was obviously talking complete 'horlix'
SA