As folk said above, the whole thing is nothing more than a collectors wet dream, and maybe get a fast lvl70 character.
Here are the following stuff you can get from it:
-Transmog that include Leveling Gear, Dungeon Gear and Raiding Gear (Which sadly aint my cup of tea cuz MoP gear is shit mostly, and no PVP gear)
-The old Garrosh Heirlooms and Tusk of Mannoroth
-Mounts (Which include new recolors and already existing ones from raid bosses, like Heavenly Onyx, Son of Galleon, Kor'Kron scorpio etc.)
-Toys and shit (Which I didn't bother personally cuz ain't my thing)
-Special Feats of Strength account wide achievements for MoP: Remix category
There are also special gems and sockets, which I don't know if they will be carried out after the remix or not but if so, these gems are mighty fine. Ranging from: Leech, Speed, Haste, Mastery, Stamina, Crit Strike etc.
Personally, I've finished all available stuff for pure f2p accounts (Except 2 factions and Isles of Thunder). And I'm now focused more on testing and running some experiments on just how broken/fucked up classes/specs can be on hardcapped stats. So far (Warlocks, Enhancement Shamans and Survival Hunters are extremely fun, rest are serviceable or just boring.)