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Flights between Boston and Washington, which already offer dual-class service, will be augmented by a 15th roundtrip beginning on Sept. 8, with Boeing 737-300 equipment. The flight will depart Washington at 6:50 a.m., and will arrive in Boston at 8:09 a.m. The return flight will depart Boston at 8 p.m., and will arrive in Washington at 9:31 p.m. Beginning Oct. 27, these flights will change to a two-class Airbus A319, and the Washington departure will move to 6:30 a.m., arriving in Boston at 7:42 a.m.
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It sounds like DCA-BOS will be returning to the A319 soon, albeit a two-cabin version.
I think the real motive here isn't so much the need for First Class on the Shuttle routes as it is the benefit of one-class Airbus aircraft on high-density Florida and select Caribbean routes. The A320s stripped from the Shuttle operation are a common site out of Charlotte and, to a lesser extent, Philadelphia to Florida and the Caribbean islands. They're high capacity and don't have First Class. I'm sure the A319s are being removed from the Shuttle operation to place them on leisure routes. And no harm to Shuttle: the two-class Airbus product is fine, and upgrades are IME very easy.
Note for non-Preferred flyers: The Shuttle routes are the only routes where anyone can purchase E-Upgrades and use them on discounted fares. On all other routes non-Preferreds need to be on full fares to use E-Upgrades.