The DoD must, by now, be concluding their study for the future SIGINT platform, after the failure of the Army/Navy E-145 Aerial Common Sensor project. It is believed that during budget hearing sessions later this year, the USAF and USN would be forced to decide whether their airborne SIGINT should be merged in one program. The Army, which needs to have a replacement fielded the soonest, is being marginalized, as its operational concept of using smaller aircraft in conjuction with UAVs is at loggerheads with the other services' requirements for bigger and longer platforms. So far, the Navy is leading the way with the proposed medium P-8A MMA SIGINT variant, while the Air Force is budget (unsure) limited to one demonstration aircraft for the RC-135 Rivet Joint replacement.
While a notional special ops E-27J could be a rugged in-theater operator, and the Global Express or G550 might be a good fit for the Army having already proven their capability as ASTOR and Nachshon base respectively, the B-736 may have an edge in commonality, given that the Navy is acquiring 108 P-8A MMAs and might also order its SIGINT variant. It might also help that its structure is already overspecified for its size and therefore wouldn't need much strenghtening. The cabin volume advantage over the Global Express and G550 would address the deficiency of the E-145 and allow for future growth. The lower cargo hold could carry additional fuel to increase range and time on station while a projected ability to deploy MAVs and operate at higher FL and farther distances in concert with UAVs might mitigate susceptibility/survivability issues. And the proposed reduced depth radar may solve the ground clearance problem.
Commercial based platforms are abhorred by some sectors but in this era of budget cuts, those are the likeliest to see the light of day.