I was talking to Holmar recently and here is what I think he meant.
That you use vending machines like boats in the mall map. We played on Lake Plasterd and he demonstrated how to pilot/steer vending machines in the water. It works pretty well.
My opinion on the idea is that some values for the human push would need to be changed. While the vending machine is pilotable as a human, the zombies can easily just catch up by just swimming.