Although I don't expect any major work to go towards anything that isn't Underrail: Infusion anymore, Motorcycles are just essentially a sprite change way from Jet Skis to be a reality.
Think about it, we already have Jetskis with Storage and the Parts System. If someone just made a Jetski capable to travel on land (and disable water travel) and reduced their travel speed, what else would we need? Most of the work would end up being spritting all the different bike models (assuming the Quad Bike isn't usable as a base at least) and timing animations to the specific movement speeds.
We'd also need a Bike Store or two somewhere and maybe an intro quest (which I expected to happen when Travis mentioned his broken quads).
