I think phllax states it very well.
The bottom line is that the A-gates were designed to handle international traffic. Since DL has no plans to fly TA from PHL, they have no business over there (especially when US has committed to international expansion). US and PHL built a $400 million terminal so that there would be room for expansion, not so that they could move domestic flights over there and redeploy the mobile lounges less than five years later.
Building a new WN termianl by 17/35 sounds like a good idea at first but, it will just mean more delays since there will be 40 or more additional WN flights. How many flights to PVD, MDW, BNA, MCO, etc does PHL really need, anyway?
One more thing: Does anyone know what PHL actually promised WN when they came to PHL? I thought they promised them up to 8 gates, but if they promised them 10+ gates, PHL appears to be in a situation where they counted their chickens before they hatched.
Just my 2 cents.