[Taylor]

Does a butterfly-style drive necessarily imply the use of pneumatics? For a robot design that does not otherwise incorporate pneumatics, it is certainly important to factor in the space, weight, wiring, and programming required for a pneumatic system to support the drivetrain.

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Also, it's important to consider levels of implementation. When I think swerve, I think 16, 71, 111, 118, 1640. Those aren't representative of the 'average' swerve drive robot.
If a butterfly drive succeeds, it's pretty nice. If BD fails, it's still a completely capable 4WD robot*. However, there hasn't really been a team that has used it consistently enough, and at a high level of success, to be the standard-bearer for that configuration.

*the same can be said for a failed SD, but mechanical locks may be needed to achieve that.