I would just like to point out that the DSi is really the first time that a revision added some functionality that made some new games not playable on the old models, and even that was largely download games that most people didn't care too much about. And that revision wasn't the first revision of the DS, it was the second one, and it was introduced about five years after the DS. Systems like the Game Boy Pocket and Game Boy Advance SP don't have any exclusive games that won't play on an older model, nor do they have any features accessible only on the new model.
If a revision happens soon, it would be unprecedented for Nintendo, both in that it's introduced very early, and that it would add functionality to games and could potentially split the userbase. So, I wouldn't say that anyone should have seen that coming, and it would be a very bad thing for Nintendo to do.