*stretched fuselage for more fuel and weapons and maybe a WSO.
*fully developed avionics upgraded to F-35 standards.
*big wings, subsonic engines for a ultra high flying, ultra long endurance strato bomber.
and that's just off the top of my head and I'm not a jet guy. These all might be impractical but hey, I'm trying and so should the USAF. I'm convinced that drones, while useful in a COIN, are less relevant in other scenarios.
Time will tell but we should maximize all the systems that we have in hand now.