The thing with Joshua is he has very quick hands (both in action and in spotting chances) compared to most heavyweights. Given that if you let any decent heavyweight catch you on the chin you're going down having someone who picks gaps as well as him means he's always a good bet to KO someone in the first 3-4. After that it all becomes a bit more difficult to predict because it's uncharted territory but if you put an undefeated world champion on his arse twice in the 2nd round you're over the 'he's not fought anyone' hump and you have to be looked at as the real deal.
I don't want him to fight Haye, AJ gets nothing from that fight right now, Wilder, Ortiz or Fury should be the ones he's looking at. I'm ignoring Klitschko because I don't think that fight will happen because Klitschko gets nothing from it.