If the Met ASU does get absorbed into NPAS, it would be very interesting to see what would happen. The Met has some very specific but unusual deployment priority criteria, certainly when compared with other ASUs. They also have an already established system to cope well with a massive number of jobs suitable for ASU tasking. They also already fly over 3,000 hours per year (between 3 aircraft), so there is not much slack to be taken up on other force tasking.
It will be interesting to see who prevails: my money would be the "comfort blanket" for the senior officers managing the high profile events.
The Met though is very different from other ASUs. They already have an really effective dedicated control room facility and in-house engineering on their solo type. It will be very expensive to absorb into whatever NPAS ends up doing. Almost inevitably less effective IMO. Worse for the Met and not much availability for other forces.
In the end it may well depend upon how the senior bods in the MET approach things. The Commissioner when CC for Merseyside appeared to have been happy to lose his helicopter, without much pressure. And I believe he was the ACPO lead for air support at the time.