Triple H, Kevin Nash, and Ric Flair are the obvious choices. Although Scott Hall and Sean Waltman would also be possible choices. I doubt they'll get the entire "Kliq" to induct Shawn, but then again, they did have Rey Mysterio, Chris Benoit, and Chavo Guerrero Jr. all induct Eddie Guererro. So I guess they could get multiple people to induct Shawn, but I think they'll stick with one guy to induct Shawn. If not it'll probably be both Triple H and Flair, not the Kliq.
As awesome as it would be for Bret Hart to induct Shawn, it's just not going to happen. Not because Bret will never return again, because I don't think that's the case. I think Bret eventually will come back to the HOF to induct someone. More than likely Owen and/or Stu Hart. I wouldn't even be surprised when they finally induct Macho Man (the signs are there now with the DVD and all the attention he's getting on their website, including being added to the Alumni, which basically means he's on good terms with WWE), if they don't get Bret to come back and induct Randy. Bret has always admired Randy (he defended him and Mick Foley back when Flair criticized all of them in his book), and he often stated on TV that he felt he took Randy's place as the top guy, so he obviously admires him and probably considers him a friend. So I'll bet if Randy Savage or Vince McMahon asked Bret to induct him, I'll be Bret would be glad to come back and do it. Plus there was talk of him inducting either Stone Cold or the Funks this year, and said he would've gladly done it, but that didn't ultimately end up happening. But I don't think Bret will come back to induct Shawn. I'd like to think that maybe eventually they'll make peace, which is possible I guess. But if they do, it will be privately, not in front of the wrestling world by a HOF induction.
But there's one guy that no one has mentioned yet that I think is being overlooked......
Chris Jericho.
Shawn Michaels was Chris Jericho's biggest role model in the business, and he modeled himself early in his career after Shawn. From his look, to his outfit, to his wrestling style. That's why their match at Wrestlemania XIX was so great. They played on the idea that he is just like Shawn, and they were mirror images of one another. Plus, they've went on to have undoubtedly one of the top feuds of the 2000's last year. I think outside of Triple H, Hart, and Taker, Jericho has been one of HBK's biggest rivals in his career. Jericho might be a suprise inductor.
Another possibility is Vince McMahon himself. Shawn has always been like a son to Vince, and he's put up with more crap from Shawn than probably any other wrestler ever. Obviously there's a close bond between the two. Vince may want to proclaim Stone Cold as the biggest star in the history of the business like he did this year. He may want to proclaim Shawn as the greatest wrestler in the history of the business. It's possible.
But ultimately, I think it will be either Triple H or Ric Flair, or both.