The responses above regarding technology improvements I think are spot on. Just as with calculators and laptops, tremendous improvements with prices dropping at the same time.

But to Tom's original question we are not quite there yet. Two issues on which I would speculate would be the width of the sensor "beam" and how to correctly discriminate peregrines from other birds in the sky at night.

Maybe the first ways to adapt technologies for night-time bird counts will come from retired military components. There is a fairly active transfer now from the military to wildlife uses, mostly to universities.