I'm working for the Space Situational Awareness Integration Office to develop the operational architecture for how the US will conduct space for the next 20 years. We're working along with the National Security Space Architect (NSSA) office in this effort. Planetary Defense has been added recently as one of our core mission capabilities. None of even the most far out architectures remotely see the need for lunar-based observatories to do the mission. It simply isn't necessary for the detection/track requirements, would cost tens of billions (and for that reason alone will never happen), and would take at least 20-30 years to implement even if it were funded. It ain't gonna happen. Period. Not only will that dog not hunt, it won't even get out of bed. You know not of what you speak.