My thought is that renewed interest in this and the not strictly confirmed but seemingly under active developement SR-72 is… … Platform for high altitude launched, satellite killing missiles. For a long time the US got to enjoy being basically the only power with a stupendous intelligence advantage from a network of spy and comms satellites vast enough to get total coverage, basically everywhere, at pretty low time lags. Well now, others have comparable capabilities. So, develop a way to remove that. We’ve been able to shoot down satellites from aircraft launched missiles since the 80s. We’ve specifically called for the end of tests of ground launched anti-satellite missiles, leaving aircraft launched anti-satellite missiles as a neat little carve out in our own rhetoric/intl. policy ‘suggestions’. So, in a world where spy and comms sats are just viewed as valid targets in a large scale war/operation, a fleet of mach 3+ / potentially hypersonic aircraft that can deny intel to the opponent and likely also gather your own intel, that’re significantly harder to shoot down than a satellite… seems like a plausible doctrine to me.