This is all completely hypothetical, based on what I believe would help improve the current raid situation.
Edit: http://us.battle.net/wow/en/forum/topic/3123313475#1 (Link to topic on official forums)
With the release of the 4th expansion:
-Attunements returned
-----Reputation to unlock BoA keys for Heroics from Normals.
-----Quests to kill the final bosses on Heroic/Normal of the raids.
-----Quests are repeatable, however the keys could be learned, and BoA much like the Lil'Tarecgosa pet where even after learning it, the "pattern" stays in your bags where you can send it off to other toons.
-T14/T15 released with the expansion, allowing true casual "progression" to occur where you finish one raid, and have the opportunity, but perhaps not the gear to move on to the next raid.
-Upon completion of T14, a quest will be completed that unlocks T15 Normal as well as T14 Heroic.
-T15 Heroic can ONLY be unlocked by completing the T14 Heroic modes, and the quests that accompany them.
-T16 Normals unlocked via completion of T15 normals, T16 Heroics unlocked via completion of T15 Heroics, etc.
-T14 Heroic will have higher ilvl gear than T15 normal.
Example ilvl on gear:
T14 Normal: 533 T14 Heroic: 560
T15 Normal: 552 T15 Heroic: 579
T16 Normal: 571 T16 Heroic: 598
In conclusion, this would create a progression path that takes you from Heroic modes to Heroic modes, and Normal modes to Normal modes instead of Normal -> Heroic -> Normal -> Heroic. MOST IMPORTANTLY, there will be less burnout from guild members. If you're working on Normal Modes, you just playing as you are now. However, if you're working on Heroic modes, the normal mode gear is now worse than the previous tier's Heroics, so you can continue to work on the Heroics until the end of the week without killing the same normal mode boss over and over and over.
TL;DR
Next expansion Attunements, Heroics and Normal raids have completely different progression paths instead of intermingled, less burnt out members in Heroic guilds.