[DampRobot]

I believe team 100 tried this approach in 2005, although I could be thinking of another team. Instead of a diamond pattern, they had 6 wheels (with the swerve modules in being the middle two of a two by three grid of wheels). I believe they had problems keeping the modules rotating together, which didn't result in a very effective system.

If you're simply looking to eliminate weight, check out some of Bomb Squad's past drivetrains. In addition to an awesome, iterated into oblivion swerve set up, they've tried 3-wheeled swerve. As far as I can remember, it had great performance and substantial weight savings.