“Fortunately aerodynamics don’t change. The B-52 was apparently a GREAT design, transcending the decades.
I’d suggest that we make some SR-71 based bombers for the future.”
The B-52 was considered nothing more than an interim design: it was an adaptation of the principles first embodied in the B-47, built larger, and with the worst vices of that hot-performing medium bomber minimized. It was intended merely as a stopgap to tide over the strategic air forces until the really revolutionary systems were developed. Great hopes were pinned on the B-70.
The B-52 has succeeded so well in part because of excellent initial design, superior manufacturing, exceptional re-engineering and maintenance, imaginative subsystem upgrades, and better software. The airframe is big enough to be really adaptable; another aerial giant, the B-36, underwent a similar series of upgrades throughout its (shorter) service life (ended 1959).
The rest has been politics and luck.
Much has been internal USAF politics: bombers have always been proportionately more expensive, so proportionately greater resistance to spending money told eventually. Also, fighter pilots took over USAF and have done as much as they possibly could, to phase out manned strike aircraft and erase all traces of bomber leadership and corporate culture.
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The SR-71 would make a ridiculously poor bomber.
It sported very short legs, and only a tiny payload. Such drawbacks can be lived with (to a point) for recce missions of sufficient urgency, and with small numbers of airframes. They would sound a death knell for any bomber.
Every design consideration was sacrificed to the requirement to attain and sustain high altitudes and very high velocities. Therefore, internal spaces very small and equipment positioning was completely inflexible. This made it very, very difficult to design and build systems to fit into little holes, the locations of which was rigidly controlled. So it could not adapt.
It was never more than a quasi-experimental system, struggling to emerge from a trouble-plagued development. It demanded special fuel that was much more costly, and never used in any other system. The vast performance capabilities created a great range of operating conditions (temperature, velocity, air pressure etc), which put unheard-of demands on internal systems and structure, making it dangerously leak-prone, a fault never completely remedied.
Low and slow airborne missile platforms apparently have a continued mission.
Until we have enough Satellite nukes, a high altitude, fast delivery platform provides an initial, selective, credible threat to actual threats (Iranian "leaders").