Think of it this way. You have your normal 5-mans while you level. Once you hit 95 (or whatever the new level cap is), you'll be able to queue for Level 95 dungeons. These instances are identical to normals, but the numbers are adjusted for capped players, and all loot has a higher item level. Players who only intend to run LFR will be fine with stopping here and moving on to those. Players who want to gear up further for Flex or normals will move on to heroics. Unlike current heroics, these new age heroics are quite a bit more difficult, and not just as far as DPS and healing requirements. Bosses could have new mechanics exclusive to this difficulty, as well as drop new loot. In fact, heroics could have entirely unique encounters that normal modes and Level 95 dungeons don't have. Basically, the encounters have more of a raid-like quality to them, sort of like practice for when they move on to proper raiding.
I didn't find the right solution from the Internet.