It's not a rehash if it is truly all new mechanics are they previously advertised.
Not all new mechanics, just more new mechanics. HM has some new Mechanics to SM, where as Nightmare is advertised to have some new/different mechanics, specifically some that make previous strategies used by many guilds no longer viable.
Which still takes much work to tweak it. The way they made it sound, making our previous tactics no longer always work - it sounds pretty interesting, if it plays out how I think it will.