News from Blizzard and currently live on the Beta, are changes to account-wide mounts and achievements. The whole system is currently up for debate, but Blizzard are indicating their current direction for mounts, pets, titles and achievements, the plans at this stage seem logical and very fair.
The design philosophy as outlined by Ghostcrawler, "Overall, we never want you to play Character A instead of Character B because of achievement concerns." also, "Having alts is cool and working on achievements is cool, but we don't the two systems to work against each other". This design philosophy is achievable but is less snappy than previous edicts "Bring the player not the class" and "The Hybrid Tax".
The benefits of this system are many fold, as an Altoholic you could have a Rogue for PvP, a Resto Shaman for healing in Raids, and a Hunter for all other achievements. items such as Honor Kills, total money looted, dailies completed will become account wide totals. Does this have an adverse effect on Main character only players, possibly but why would want to do more than 25 dailies?
I personally will benefit greatly from this new design. In WotLK, I raided Ulduar, Trial of the Crusader, and Icecrown Citadel as a Resto Shaman, I PvPed as a Death Knight, and collected achievements on a BM Hunter. When MoP comes out I will collect a load of new account-wide achievements from this expansion. In Cata I have mostly raided, PvPed and achievement collected on my Hunter so there will be very little benefit.
Mounts will save altoholics a King's Ransom in gold. The main gold sinks of Mekgineer's Chopper, Traveller's Tundra Mammoth, and Vial of Sands. will now be available to all your characters. In addition throw in the RNG mounts from the Holiday achievements and you are looking at Kodos, Rams, and Reins of the Headless Horseman. Of these I look forward to having a fiery flying stead on my Death Knight instead of a Paladin but then again thats why this is random loot event.
Now the 3rd type of mounts which is currently avaialble on Beta but probably will not make production are the profession only mounts, Flying Carpet and Roflcopter. The likelihood is they will appear in your stable of mounts but will be unusable without the required skill level.
The 4th type are the Class based mounts which are awarded to Paladin and Warlocks. What will happen to these mounts is as yet unclear.
What is clear is that Blizzard are attempting to give players more choices in game. How to play the game, and what we look like whilst playing the game (Transmogrification). I feel sorry for the x-mog fans as they have 5 more levels of constant gear changes in the upcoming expansion.