You are lucky to fly through airports where mobile passport is available - when I go to GCM I have to fly through CLT and they don't have it (yet).
Global Entry (which I have) is a massive, massive help there, though.
I have Global Entry and it is wonderful, but it usually only works in the US, a universal Global Entry program would be great.
I just did a search of my old emails and found the one below from 2015 from Melissa Ebanks, Manager at GCM airport - before the redesign and construction had even started.
We had just had an awful trip home from Cayman and I wrote a note to the GCM Customer Service suggesting that they accept TSA status when it has been conferred by the US Dept of Transportation. And/or to allow US visitors that are returning home to go through US Customs and Immigration in Grand Cayman - like they can do in Nassau.
She responded that it was unlikely to happen and that they would defer to the UK authority in making such a decision.
However, Cayman Air recently opened a Cayman Customs and Immigration process in Miami airport at the departure gate, to pre-screen visitors to the island before they even arrive and reduce incoming lines at the airport - so maybe they are finally starting to explore some new options to make things move more efficiently. We can hope!
"Dear _____________,
We appreciate your sentiments.
The Cayman Islands Airports Authority has reviewed the processes needed to implement such procedures at the Owen Roberts International Airport and our findings is the limited physical footprint. These limited quantities, at this time, is an unsustainable amount of traffic to support the facilities, expenses and human capital needed to run a preclearance operation. However, should the Islands incur the footprint volume needed to consider such services we would first have to have the support of our regulatory body, the United Kingdom (UK). If it was then authorized from the UKs end the next step would then lie in the hands of the United States Government for TSA to decide if they support the Cayman Islands in being destination to hold the TSA preclearance status.
Even though we are not here yet, we do hope that these processes needed in order to visit our Islands will not hinder your decision in continuing to make us your destination of choice. We appreciate having you here and look forward to welcoming you again.
With warm regards,
Melissa Ebanks
Customer & Commercial Service Manager
Cayman Islands Airports Authority"