Something that not even necessarily deems to be beyond the realm of possibilities, a mod that illustrates a ghost car of a player in someone else's game using their game save. I remember Hard Drive doing something like that.
I think that used to be called 'demo'. An other name would be 'replay' or 'recording'.
That is of course doable, as in recording your own positions and replaying them. To have meaningful triggers, however, it would need something like recognition when you started the run so it starts to play it.
It is all doable, but I am not sold on working myself in that direction. Being online and seeing someone else who plays live sparks much more joy in me. In conclusion, we can post it in mod wishes or such.
My thoughts were going toward two instances of the game talking to a cloud server that lets both of them know where the other player is with their car, and subsequently having the ability to insert that car in the game (non-mods). I would support work on such a mod with my own work and money for hosting servers.
Running backend multiplayer servers in the cloud costs money, and my guess is that it's one of the reasons Cyberpunk 2077 never saw multiplayer experience. Besides the stated problem that they couldn't even organize the police chases better. There must be some significant limitations I am not full aware of, but at my level I don't perceive a problem of two, three, four or more players being on the same map... anywhere. It could only be that there won't be need to show them to each other before they come close enough, but still some 3D tracker arrows can be placed in the view/Kiroshi HUD, so you can have an idea where your buddies are on the map. I think those things absolutely possible.