alt Hacker NewsChina can launch a lot more than a dozen balloons, perhaps thousands if convincing decoy payloads can be made. The A-12 was intended to counter high-value targets in a limited number, not low-value targets en-masse.
I can't rule out that Issacman does have this mission profile in mind, but it seems contrived. Whatever weapon the SR-71 could carry to-altitude could be be done cheaper, more numerously and probably more quickly too with F-15s. Refurbishing a fleet of SR-71s and a fleet of KC-135Qs would be a lot of work for an extremely limited capability.
F-15s are not stealth. You don't want to risk escalation by sending fighter jets towards someone else's airspace. To me, they don't make sense for this kind of mission.
It does sound like a lot of work, but that's the part of the puzzle that is not a mystery. Someone is in fact putting one of those back to work, we just don't know why.