Some things to think about. Weight of a swerve drive is often very heavy trying to reduce the weight is a major chore.
Just to keep in mind. The closer your gears are to the final reduction of the drive train the more or a moment they will be taking. This can be come a huge problem when you take large amounts of pushing or something unexpected. The moment is directly related to your wheel size.
Also remember your whole robots weight will be carried through the upper gear box this can cause major problems for thin metal flexing and losing gear spacing causing them to skip/bind I like belts for this reason. The competition is not the most ex-stream things that will happen some one might drop it and one of the poor modules will take the load of a potently 150 pound robot falling from 2 feet. I like belts for this reason.
My team has been designing a swerve drive using the same duel wheel concept.
http://imgur.com/a/H6Qcm
The main goal over the old was was to reduce the size/ machining complexity/assembly complexity/points of failure/ and the biggest was increasing mechanical efficiency.