Citizen United was about political speech, not selling cars. There's a long history of the court taking differing approaches to commercial speech vs political speech. Ford most likely could open up stores to distribute political literature. They could even likely make a Ford movie. What they can't do is sell cars.
The court generally errs on the side of the people when it comes to political speech and on the side of the state when it comes to commercial speech. I don't see Ford having much of a case opening up dealerships under Citizens United.
The other model that some legacy manufacturers are working on is to let customers go through the whole purchase process on their corporate web site and then just take delivery through the local dealer. The dealers are happy with this arrangement since they still get to profit on the sale and don't have to do any sales work.
Can Ford not put vehicles in public areas with associated literature (paper marketing, iPad kiosks, etc), and take orders from that mobile device or via a customer's phone?
The order takes place where the servers are (the same as when you buy a Model S on teslamotors.com), and you would be prohibiting the corporation's freedom of speech (finally! a use for Citizens United that sucks less) by preventing them from putting a vehicle out in public (if they have approval of whomever owns/controls the underlying space).