BMWs have had this, to some extent, for a while. Bimmercode can do things like change sounds and enable software disabled features, like anti dazzle lights. (This is disabled because the NHTSA refuses to adopt ways for them to be easily tested in the US, despite their being approved for decades in Europe and a congressional mandate telling them to allow them on the roads, so every automaker has to disable them.)

No exploits needed.