Taken from the front page of mmochamp.Faction specific mounts are account wide, but you can only use them on characters with the correct faction.
Does that mean as a mount collector I have to max rep and do the argent tourney ground on both an ally and a horde toon ?
What im taking from that quote is that my horde mounts will show up on my ally toon but be basically unusable. But at the same time they will be increasing my mount total count on that toon.