There's a few classic cards that are problematic or overly powerful to the point that they almost always see play in every deck for that class. For example, Wild Growth, Sorcerer's Apprentice, and Preparation have all pretty much been must haves in nearly every deck for their respective class for the last 3+ years, so any/all of these are likely candidates for the hall of fame. Then there's cards that aren't exactly super powerful but are problematic because they limit design space. Prophet Velen is a perfect example of this and because of his existence, priests are extremely limited as to what kind of damaging spells they're allowed to have. There's also pretty much every minion associated with Charge. I can easily see Stonetusk Boar, Southsea Deckhand and even Leeroy Jenkins going to the Hall of Fame because I honestly think it's a keyword Blizzard wished they never printed (in fact, I seem to remember reading that at some point). I saw some mentions of Mind Control Tech and I do feel that that is a contender as well. And lastly, possibly Alexstrasza, even though she's not seeing a whole lot of play right now.
Now while I doubt that all of these will get hall of famed, I wouldn't be surprised to see one or two get the axe come April.