The whole of the SR-71 was built around what kind of cameras was needed to perform the mission. Modern electronics and cameras are much smaller. I would presume an unmanned plane launched from a bomber could perform the mission today.
Satellites are predictable. The mission is unscheduled surveillance.
Most modern spy satellites are low observability. Combine that with overlapping coverage and the only thing you can predict is that there’s probably a satellite capable of looking at you right now.