Just imagine: 'challenge mode' raids that award a special currency for either transmog gear, mounts, titles, or some other nifty benefits such as the Blessed Medallion of karabor.
While I appreciate the comfort of storming the citadel alone for transmog gear, It would be an huge asset for the game as a whole if someone could access the old content in a way that was still challenging. Older raids had different 'tuning' since raids were thought differently, only 10 or 25 players, only shaman could use heroism, healers were supposed to refill a tank in 2 heals because the damage intake was incredibly high. As someone who is following strategies for Herald of the Titans: no, staying 80 is not just as simple as that: class mechanics, stat, abilities, and synergies have changed.