Problem is no one would do it unless there wasn't an easier alternative. There would have to be exclusive items/content obtainable from something difficult like that, or people would just stick to whatever's easier.
edit: well no, you have plenty of people doing Diadem HM over NM, but that is mainly because HM is so much more efficient for getting 210 gear. If you could get xp or items more efficiently in a difficult and dangerous zone people would probably use it.