Patch v5.40 is live, StormShieldOne has posted their datamine findings for the Patch. In these findings we see an option to set a Random Battle Bus.

Similar to the customization options for Skins, Loading Screens, etc. An option for a Random Battle Bus is in the v5.40 files. It is likely Battle Bus customization will be a part of the Season 6 Battle Pass.

Randomly chooses between favorite Battle Buses (or all owned Battle Buses if nothing is marked as a favorite)

It appears that StormShieldOne has discovered a Purple Battle Bus which will be a Battle Bus Customization option.

"fortnitegame/content/athena/items/cosmetics/battlebuses/bbid_purplebus.BBID_PurpleBus" = { DisplayName = { Text = "Purple Battle Bus", Key = "F3DFF673450DC68A639549BC84D9318B", }, ShortDescription = { Text = "Purple Battle Bus", Key = "E5A456774FA5292B05FD248CED539B87", },