First of all, I think it shoud not be called Great or Greater Hungary but Historic Hungary. And the second thing I will add is, that Kingdom of Hungary was not a national state of Magyars in any period of its existence. They have never been a majority in it and the fairy tales like "Hungary 90-95% Magyar in midle ages" lacks elementary logic.
So the conlcusion is: Restoring kingdom of Hungary in its preWWI borders is unreal. Anyone, who raises such demends should realize, that the only way is war. But who really wants another white-on-white slaughter in the middle of europe? The true victors of such war would be gypsies and jews.