PNC stock trades at about four times the value of a USB share, so there won't be any acquisition of PNC, could very easily go the other way, but PNC doesn't need a midwestern footprint, nor does any other regional bank, it's already a crowded but slower growing region of the country.
Regional bank c suites and boardrooms are well aware of the wall street analysts' published concerns regarding the laggard USB banking franchise, partially caused by lack of true banking leadership and focus on the novelties that cost a lot of money and don't generate revenue or otherwise move the growth needle, such that most will steer clear of any USB overtures, preferring other better managed and growth capable banking operations, not burdened with the tons of baggage USB brings to any merger/merger of equals/stock swap acquisitions.