Much as I like the idea, it would be difficult without a large base of landowners who can afford to keep horses.
Remember though, for it to be popular, gambling needs to be associated with it
Not really, for several reasons:
1) You don't have to have heavily armored knights on incredibly expensive destriers. You could have guys in light padding on regular riding horses, using blunt and heavily padded lances.
2) When you consider the cost of maintaining today's baseball/football players, maintaining horses (even if you DID use super ones) is a pittance. You've got some pro players paid $10M+ per year -- you could maintain a pretty large group of knights and horses for that.