I am a massive fan of account wide features, in part as bit of alt junkie but also as long time diablo player. It's always nice to obtain items on your main character that you don't need and simply send them to an alt that does. One of the biggest barriers to alt content has always been time, while it's fairly easy to achieve the mandatory gear thresholds and attunement quests on mains. It becomes a massive time sink and not very fun to have to repeat this across multiple characters. This harms the game in both the short and long terms, in the short term it effects participation and queue times. In the long term it can affect the desire to keep playing.
Now giving blizzard there credit they have begun to move more stuff to account wide, in 6.1 we got heirlooms which was fantastic. Previously we have received achievements, pets and mounts. Also the legendary ring quests have increased drops on alts when your main has completed it. Which is brilliant, in a similar way to the cloak in MoP there is no way you would not want to have the ring on every character possible. As well as unlocking Garona for all your garrisons. Yet both quest chains are fairly intensive time wise, I hope that with the arrival of the next raid tier they increase the number of bosses that drops Stones and Runes.
All of the above measures are good; however I don't think that this goes far enough. The time has come for the floodgates to be opened and for as much as possible to be made account wide. From Banks and storage to Reputations to tabards. Maybe even gear from outside of raid content. Fundamentally I don't think that Wow is ever going to attract a massive intake of NEW players. After ten years the time has come to focus on quality of life for the existing player base. By making the content easier to replay multiple times through. (It could even be as simple as decreasing requirements based on the number of times you have completed it.)
A prime example of this was the timeless isle, as a piece of content it offers both lots of new top end content world bosses and rare hunts as well as a rep faction to grind. But it also offered people at the bottom end of gear progression a means of catching up. Or for people with many alts a shortcut to getting them geared to a reasonable level to run group content. If I have only one character geared for raids I can only run that raid once a week if a I have 6 geared, while I may not choose to run it 6 times. I will probably run it more than once thus adding more bodies into queues and groups finders.
Now the only major negative of masses of account wide features is the possibility to trivialize the content. But in my opinion making it easier to RERUN content multiple times has little impact on its value to a player who only runs the content once. Or more simply as long as the first time through the content takes time and is meaningful. It does not matter if the 2nd time it takes half that long to complete and the third time it takes half again. For example the WoD quests are fantastic, yet now on my eighth time through I no longer watch any of the cinematic or even complete the zones. My sole aim is to complete the levelling experience as fast as possible. In this situation there would be no issues in having a massive experience buff for alts after you had completed the quest the first time.
In many ways as the game continues to move forward and evolve, we have reached the point where the fact that many features aren't yet account wide is absurd. For my final example I am going to use the WoD reputation factions. I have 7 level 100's yet despite this I only have one maxed out faction, because the rep grind are long laborious and ultimately worthless. The removals of gear from reputation vendors while a good thing. Has left the Reputation vendors with very slim pickings that barely justify the time and effort required to get to exalted on one character let alone multiples. I for one really liked the championing a faction system from MoP, it was a nice daily bonus and gave you another reason to run 5man Heroics. WoD could use this, because at the moment rep grinds are endless and dungeons have no value.
So coming up next I am going to wax lyrically about Seasons in Diablo, after that it will probably be a reflective look at hearthstone and how it's so much better on tablet/phone. The week after that it will be either the state or raiding, or look at 6.2 and the ramifications if we only have two tiers of raiding. Though of course the orders could change.