What is the possibility on them using prequel cameos like how PJ used Cameos in the Hobbit films of actors from LOTR?

I would prefer they did not do so.

They don't have to make fan friendly references to the prequels when they are trying to get a new audience nor can they simply ignore half the films that exist.

I may be wrong and JJ may indeed ignore the prequels. But i doubt it from interviews i have read in the past Kasdan never struck me as much of a hater of those movies. He may have disagreed with some things from Return of The Jedi to the prequels but was never a basher or a hater and always praised Lucas.

Some things obviously won't make a return if they are smart. No reference to midi- clorians, no Sith rule of two, no prophecy. I do suspect that Sith and the Empire will be in the movies though.