I would love at least 1 (out of the two dungeons we get now) to have a non-linear design, it'd be a nice change of pace. The problem with it though is that, as said before, the "high-end" players would find the most "efficient" way to clear it with the least amount of work, and everyone would mindlessly follow their example, and we'd never be given the option to take another route. How often do you either choose to, or give others the choice to take the alternate paths in, say Dzemael Darkhold for the treasure chests? Or the extra rooms of Toto-rak, or Haukke Manor? It'd be wasted time for the developers to give it, because this community will NOT ever use it.