See, here's the thing:
Whatever "cost" US currently absorbs by operating at PIT is passed onto the passenger thru higher ticket costs. The PFC will still be passed on in the form of higher ticket costs.
Further, that's money that can't then be used for things like terminal/runway/hanger improvements. What's the bet that if the ACAA is stupid enough to do this, U will come back in 3 years and want a hanger/hangers for the MDA aircraft (a la the debacle for the years prior to the failed merger with UA)?