The reasons light rail to the airport doesn’t make sense today are basically the same as commuter rail, and they all still hold true (see previous discussion).
But if you meant like the AirTrains in New York/JFK, Newark, and San Francisco? I mean that’s true as long as you can secure a good right-of-way. But:
That’s not a question for Raleigh (which is what this forum is about), but it’s a direct interest of the airport.