It's boring, but "aerial hypersonic testbed" is almost certainly NASA's intention, just like they did in the 1990s: https://en.wikipedia.org/wiki/Linear_Aerospike_SR-71_Experim...

This is a NASA/JPL project; there are a limited number of airworthy SR-71s, they are not modernized for combat, and they cannot scramble to intercept. The M-21 variant has a well-documented conversion to a mothership[0] that can ferry payloads externally to-altitude and at high speed. This is incredibly ideal for testing captive ramjet/scramjet technology, since they require Mach 3+ speeds to attain ram pressure through the engine.

Sending the SR-71 into denied or uncontrolled airspace seems like a terrible idea, in 2026. Chinese and Russian naval interceptor missiles could shoot down the plane at it's maximum speed and altitude; it's not going up against 1980s missiles anymore. The risk is absurd, and there's not enough SR-71s to treat them like they're expendable.

[0] https://en.wikipedia.org/wiki/Lockheed_D-21