Mark, I don't understand why you believe cross bunkers are irrelevant today.
I've seen several examples of cross bunkers which are very relevant to the scratch or professinal golfer on modern courses, most noteably at Wolf Run outside Indianapolis, IN and Persimmon ridge in Louisville, KY.
Perhaps the question should be, "must a cross bunker be all things to all golfers on a particualr hole?" In other words, it may be that on a particular hole the cross bunker affects (mostly) the highly skilled golfer, while a cross bunker on a different holf affects (mostly)the less skilled golfer. Would such emplotment of these hazards be equitable? I don't see why not.