We're working on a change for a future patch that will make it easier to gain reputation with a specific faction on every alt on your Battle.net account, after you reach a certain reputation with that faction on another character.
Stay tuned for more information on this, likely coming before the end of the week.
Why not just make rep account wide like with mounts and pets? Reputation only works as an interesting game play option when you are of the mindset of only playing one character. As soon as you consider alts and the rewards they might want, Rep becomes the most ridiculous aspect of the game imaginable.
On top of which, there are several achievements associated with reputation, of which all your characters get credit for on the achievements panel, but no credit for when it comes to actual game play. Add to that the fact that of all the brand new mounts in the game, the cloud serpent mounts require rep gain on other characters in order to be used by them.
It's literally like saying 'oh hey, we made your mounts account wide, except the cool new one that you might really want to use on your other characters.' I made the mistake of leveling my druid to 90 first, and I don't use mounts because flight form is more useful. For me to grind cloud serpent rep is pointless on that character because I'll never use the mount on it.
My main issue with these kinds of development features, is that it doesn't seem like you guys put enough thought into them. Was there not someone on your team who said 'hey, we should jot down every existing feature we might make account wide in the future, and get it all done at once so we can work on other things.'
Things that should be account wide:
4. BoAs (including BoA items aside from gear)
And probably more I am forgetting. The fact of the matter is at some point many of these things will no doubt become account wide through some 'new feature' you guys decide to add to the game in the near or distant futre. While the logistics of reserving features for later implementation might seem like a great idea to keep the game fresh, it only makes people /facepalm now because they can think for themselves and question 'well why didn't they just do this too?'
It could be a matter of budget, of time frame, and/or lack of ideas, but one thing is for sure: the current iteration of 'account wide' feels very half done in some places. In his spare time and for free, an addon developer can put together a UI that looks/functions miles better than the stock UI, and build into it a feature which can tell me exactly how much gold I have on all my characters, but 8 years later Blizzard doesn't even consider updating the UI OR adding that sort of feature.
It's just mind boggling sometimes.