well my main thoughts on this subject is that so much content in the game is put to rest when new stuff comes out, even in the same expansion, look at all the 5.0 reps and content..5.1 already trumped it, and 5.2 furthers even that, unless you level a new alt to 90, most likely you arent going to see a lot of the content that 5.0 offered, there are people who have 5+ 90's, and for them even the content in 5.0 feels months old (well it is technically)
Now look at cata content, wrath, or even tbc/vanilla stuff...who honestly goes to azeroth and explores or does anything out there anymore? the only reason to quest if you arent leveling an alt is loremaster, or 1 off achieves, none of the old content is relevant anymore, and 99% of it is skipped or leveled through so fast that it feels really hollow and more of an annoyance than anything to have to push through it again
I think really they should bridge the old content with new content, as we get new content even in 5.2, go back and breathe some life into vanilla, tbc, and wrath stuff, its not as easy as creating a team to do it (in my mind it is) the main reason why they don't is because of time constraints, the developers focus on new content, rather than old, and i think at some point they should shift some attention to those old continents and raids, the new pets in 5.1 from old raids is a small example
if you have a level 90 toon and want to go back and get all the tbc, wrath, and cata reps done, its a significant time investment, especially reps such as Keepers of Time, which takes MANY runs of normal/heroic Durnholde/BlackMorass till exalted, I'm not saying there shouldn't be effort but i think they should revamp/revise/improve the entire system for non-mop reps/content
They should apply the commendations to everything pre-mop, that would be fine to me, so my alts can aquire all the blacksmithing plans from all the vendors, such as Karazan, the tbc reps, wrath reps etc...being able to aquire all the jewel crafting patterns from say Sunreavers out in Queldanas Isle, there is a ton of them, i would grind reps if it was at least the 100% commendations, allow alts to catch up, so can aquire and see/find/do the old content
They also should re-vamp all the old raids, but leave the originals as an option, i think they should have gave us the option for deadmines, sfk etc. Imangine if Molten Core could be updated to 90+, make it into a 10 or 15 man raid, new loot, or vanity loot, keep the original drops the same but add new stuff too, more pets, mounts, give us a reason to run them again, properly (not just soloing them) hell all they would need to do is add loot/stuff to drops, and scale their health to mop levels (like molten giants instead of having 120k health...have like 5 mill or 10 million, and hit as hard as they should for a level 90 raid mob) I'd be happy with just scaling the old raids, would be rather simple to do imo.