We touched briefly on this subject in another thread. Would it make more sense to have a linear progression curve within your chosen difficulty. For mythic raiders for example you would go from one mythic tier to the next mythic tier. Going "back" for a lower difficulty than the one you are doing would be a thing of the past. The only time you would be doing other difficulties than the one you want would be in the first tier of an expansion. The raids themselves could have tighter gear checks and drop less loot for example in order for them to last longer.