It surprising how little conversation there has been here regarding how much a particular drivetrain will limit ball interaction mechanisms.
With a drivetrain which covers an entire side of a robot (6WD, 8WD, tread) you largely lose ability to manipulate balls on that side. (owing to bumper height and ball incursion rules) With a 4WD system (mechanum, holonomic, swerve, or tank with modified CoF) a mechanism can exist on any side of the robot.
To example this I've been mocking up a prototype bot designed to be able to guard the goal.
with 4WD you can park it in front of a goal, raise a shield, and utilize a kicker which extends between the wheels. Should you need to get to the other goal your already oriented to do so. High CoF wheels in the rear provide shoving power and increased turning while the front wheels with moderate CoF keep the robot in a line and add to pushing power. A gearbox + motor for each wheel allows for dynamic power shifting between the different CoF wheel sets.
While much discussion has been devoted to the maneuverability of crab, holo, and mechanum, a 4WD using the kitbot frame,wheel drop downs, and wheels with different CoF (roughtops and modified kit delrins and or rubbers) you should have more than enough maneuvering for most teams. (not to mention the cost and complexity advantages)
With regards to high siding a robot, with a 4WD system and a bottom plate, without any modifications you can and will high side.
However if you install a simple textured drum in the middle of the frame which extends slightly below the skid plate and drive it with a window motor you can effectively crawl to a point where at least one set of wheels gains traction again.