I'm not convinced that propagation delay when associated with fine adjustment of SIGINT equipment, particularly where accurate direction-of-arrival is needed, makes them 'ideal' for such a role.
Beagie, are you seriously suggesting that a 21st C. SIGINT platform must have people aboard twiddling frequency tuning knobs?
... This direction-of-arrival business: do you have in mind a loop antenna that physically rotates atop the fuselage?