The only thing unusual is that VA was Virgin America’s registration. But then again, at the same time, other carriers have this. United has some of Continental’s registrations, I believe. Delta and American both still fly Northwest and US Airways registrations respectively.

If Alaska was to follow through with the A320neo though, I’m sure they’d register it under an AS/AK registration.

Generally, planes that change ownership within the same jurisdiction (N -> N in this case), don't get re-registered. It's a lot of paperwork, money, paint, etc, for nothing but a new license plate. A surprising percentage of the flying public don't even notice the name of the airline painted on the side of the plane, let alone the tail number, let alone the letters at the tail of the tail number. UA doesn't even use the letters.

Like you said, during mergers planes don't tend to be re-registered. But even more than that, they almost never are if the expense can be avoided. Look at Delta's 717 fleet, the vast majority of them were bought from Southwest after Southwest acquired AirTrain. Through all those transactions, the planes still all have "AT" at the end for AirTran.

I think you're right that any A320neos would have *AK number, mainly because those those aircraft still haven't been allocated numbers. N929V and N930VA were both allocated before the merger. For the record, my money is still on AS cancelling those future Airbuses, but you never know. The MAX debacle still isn't over and we won't know how bad the lingering effects of it really are for several years.