The more I look at it, the less Shuttle America makes sense for UA. Right now SA has no routes that would work as useful feeders for united. Nothing to Washington Dulles or Chicago O'Hare. They would have to REALLY add service because these are the only current destinations they have

Bedford/Hanscom, MA - BED

Charlestown, WV - CRW

Cleveland, OH - CLE

Hagerstown, MD - HGR

Fort Wayne, IN - FWA

Lansing, MI - LAN

Lexington, KY - LEX

Lynchburg, VA - LYH

Pittsburgh International - PIT

Roanoke, VA - ROA

Toledo Express Airport - TOL

Trenton/Princeton, NJ - TTN

Williamsport, PA - IPT