A Halbach Array has essentially no magnetic flux on the back side. But neither does a properly designed conventional rotor. In the case of the iron backed rotor one would lose flux if one embeds the magnets in the iron. Yet in the Halbach Array that is the case, as the pole magnets are embedded in the array. So, the question is, "What would be the effect on the flux by replacing the pole magnets with blocks of iron and then gluing the pole magnets to those blocks?" Well, in an alternator, where the flux paths are well defined it is obvious that placing half the magnets sideways really doesn't change the issue. Each magnet will make it's contribution to the flux as though the other magnets were not there, if the iron remains on the linear part of the B-H curve. But therein lies the problem. Modern magnets are so powerful that the arrangement would result in magnetic saturation and a waste of magnets.