Oops, should I not have added an "other" option? If people bet on that because they think, say, Ford is going to deliver on this, and then I add an explicit Ford option, that would be unfair, right? Is it too late now, and we're stuck with betting among these 4 specific companies plus "other"?

Is this a question of what is permissible or what is possible?

Permissibility would probably have an overlay of vehicle code/law, in which case, this question may make more sense of what is possible, but strictly speaking it is already something that is possible, although perhapse inadvisable.

I'm thinking mostly in terms of permissibility. The spirit of the question is which company will let me actually do this for real in a car I own or could own.