not gonna happen.. unlike gw2 mount all the same speed at max.. and the difference between a untrained mount and a maxed mount is rather big. a event like this would be unfair for new player and pointless for old player.
p.s. gw2 have several different mount, but they all have different ability and speed.. which is why it is ok to do it in gw2..
I expect when (if) we get racing, it'll be like a steeplechase-type race, where there will be obstacles to jump over/get around, and in this game, probably monsters as well. I hope we get a new mount for finishing the race, but knowing ZOS, probably not. https://en.wikipedia.org/wiki/Steeplechase_(horse_racing)
People already do racing in eso, same as there is mount racing and non mount racing. You would be surprised what people do in Grahtwood. Just go in Grahtwood and ask around if anyone is doing their own racing events there in zone chat, you may or may not get a bite right away.