Both engines in a pod failing simultaneously is, i would have thought, still less likely than a single engine failure. Could some sort of barrier between them not be engineered to protect one in the event of the other shedding blades/disintegrating.
I thought that B52 re-engining proposals were based more on fuel & maintainance savings - JT8s are not the youngest or most fuel efficient engines out there. I assume a reasonable gain in range would also be achieved. Also the aircraft is still left with 4 engines, giving the sort of redundancy required on military missions.
My hypothetical 4 engined A320 proposal would have had newer engines - Perhaps even BR710s - depends on the best fit for the airframe requirements.