Originally Posted by corporate-wage-slave

Yes, the ESTA situation wasn't well explained at the time and the rescinding of ESTAs was clunky. Since then it first improved and now appears to have stopped.

There is a stage when airlines arriving in the USA need to get clearance from the DHS that each passenger can be landed, and in the case of ESTA there is a handshake process. If the handshake isn't given then the airlines often resubmit until it comes back OK. In the early days of the Proclamation the CBP, an arm of the DHS, was concerned that people would land on an ESTA and be cleared semi-automatically via the various borders, where staff may not pick up the impact of the Proclamation. This may seem odd, but if people were arriving from Belgrade that was OK, people arriving from Budapest would not. Instead there was some sort of pre-clearing at airports by local DHS staff or agents and the ESTA basis of entry was no longer relevant. As noted, airlines that submitted passenger lists to the DHS several days before travel ended up with cancelled ESTAs. In some cases it was because people had not cancelled their reservations, in some cases they had but the passenger lists were slow to be updated, in many cases BA cancelled the flight after sending in the data to DHS. Many airlines were affected, not just BA, and a few months afterwards there was a manual (but slow) process where ESTAs could be reinstated if they had been no intention to travel. Those who didn't do this were also able to get new ESTAs without issue.

Now if someone booked a flight this morning and turned up at LHR for a USA flight I think there is a chance their ESTA could be cancelled but that would be understandable. But I don't think it has happened recently and plenty of UK spouses of USA citizens have legitimately used ESTAs in recent months to enter the USA.

In terms of the original question I don't think there is any harm in making bookings now. There isn't any real point applying for an ESTA now or adding it to your booking, you can and should do that a week or two before departure, if only to extend the ESTA validity. This is assuming that an ESTA is almost certain to be granted in normal circumstances. Clearly if there are factors that complicate an ESTA (such as visits to Iran or criminal convictions) then you best apply sooner in case you need a Visa. So you can make the booking and there is a separate point as to when to apply for an ESTA and third stage when you add it to the booking, along with your address in the USA.