The E-190 has a larger cross-section than the EMB-145 or Saab 2000, but narrower than the A319 or B737…
Maybe the idea would be to have all your AEW/MPA/ISR platforms in a common airframe with your transport aircraft?
Could a KC390 be wired for all the sensors, which are then loaded on as required per mission? Such as this system from SAAB:
http://www.saabgroup.com/Air/Airborne-Solutions/Airborne-Surveillance/Signals-Intelligence-SIGINT/AIRTRACER_FLEX/
This might be more difficult for AEW, which usually requires other airframe and control surface changes to accommodate the large antennae, and MPA missions which require weapons delivery etc…
It would certainly make it easier for small airforces to be more efficient by operating fewer types of aircraft?