Also, I think F9, at some point, wants to restore it's service on PHL-DEN so might not want to even think about a TTN-DEN which would be quite long from a small airport anyways. Maybe if TTN establishes well in a year or so, people become loyal pax to F9 brand from the PHL/TTN point of sale side, these customers would support PHL-DEN to reach DEN or the west, in general, wanting to accumulate miles/rewards on F9.

Since Virgin America came to town, the transcon fares have dropped. But, if that carrier were to drop service, it'd make sense for F9 to return right away. The lower yielding PHL pax would be fine changing planes in DEN to reach the west, over an expensive transcon which would happen when US and United raise the fares.