This beta update introduces early support for vehicle interiors/cockpits for the Ride Your Vehicle™️ mode. The update is primarily intended for modders so they can start preparing their mods. However, some Tier 1 vehicles already have interiors implemented (thanks to scailman!) that you can play with and use as examples for modding.
Interiors serve only a cosmetic purpose and have no impact on performance during normal gameplay.
Note that having an interior is purely optional and is at the modder's discretion. Additionally, setting an interior will not affect older versions of the game, so you can safely update your mods for the beta branch without fear of breaking the default branch.
Modding guide by scailman: http://docs.voxeltycoon.xyz/guides/content-mods/creating-vehicle-interior