I think that the Town of Ewing's plan is that if Frontier works out, they will build a new terminal south of the runway, with a nearby "Town Square" type shopping center next to the airport and extend the rail line. But that is 5-6 years off at least.

Personally, I doubt they will get enough passengers that way to make it economical. It is a suburban airport; those who may lack wheels to get there, perhaps in center city Philly, are going to take mass transit to PHL.