Gretzky was the last one to have the waiting period waived. He got in immediately to the point where they did not induct anyone else in 1999, just him. But then they made the rule that this would be the last time. Granted, they can also make the rule that people are eligible again.
If I recall, the only ones to have the waiting period waived were Howe, Rocket, Beliveau, Orr, Gretzky and Lemieux. Correct me if I forgot someone. Sawchuk too, but that is probably because of his death that ended his career. Even Bobby Hull had to wait three years. Doug Harvey too.
Maybe it is for the best. I know when they placed the rule in the idea was that Ray Bourque was going to be one of the guys that they would have waived it for. But if you go back to picking and choosing it might open up a can of worms in the internet age. Would Crosby, Jagr, McDavid and Ovechkin be the types they would waive it for? Probably. But they won't, and I am alright with that.