I am transit rider in San Diego and didn't even know about the shuttle option from the new consolidated rental car facility (ConRAC). The really long-term plan is to build a multi-modal transit facility in this area to serve bus, trolley, Coaster, Amtrak, and CAHSR passengers. The current rental car shuttle with its circuitous route around the airport perimeter will eventually be replaced with a people mover under the runway to the terminals.
Locals have long complained about the lack of direct trolley service to the airport. I guess this is the first step, but it could be better. I'm not sure how many people would be willing to walk the two long blocks from the Middletown trolley station to the shuttle pickup/dropoff shelter, versus the original method of taking the 992 bus from the Santa Fe Depot.
I am not a daily trolley rider, but I don't recall seeing airport workers or anybody with luggage boarding or disembarking at Middletown station.