I came up with this a few days ago so hear me out. Lets say you're one of the guys that don't want to switch your main toon because you have done so much on him(titles/feat of strength) Blizzard could implement a system so that if you gain a feat of strength on a character that will then go over to any existing characters as well as new toon's.
Lets say you got champion of ulduar or the immortal, now when you make a new toon you wont get those right away but you have to be the appropriate level to use it (lvl 80) Same goes for scarab lord (lvl 60). When some people make new characters they want everything to be fresh and new and have zero achivement's but since most feats of strength are not obtainable anymore this system would be kinda good. As for mounts they could make that account wide as well but maybe not mounts that are still obtainable.