I hear ya complaint, and I suppose I have not noticed b/c I don't have "Lock Playing Deck" enabled so when I preview a song, I WANT TO LOAD it, not a separate preview-- I want to to go to an actual deck.
So I would not see any benefit of a preview based on the way I mix. If the feature was added, I would not use it, and I know several DJs who feel the same.
Also, the crossover sensing would not work at all based on how people generally use the crossover. My crossover is all over the place, and hardly to one side unless I am about to start cutting and scratching.