The first end game Horde guilds to have level 60 paladins (and Alliance guilds with level 60 shamans) will be at a huge advantage for raiding. There are so many encounters where having just one of the other class helps a lot.
I might even level a paladin. I'll make a hot BE chick and call her Frasskette.
Regarding hero classes, I think Blizzard already stated that they've abandoned that idea in favour of giving each class a few really good crazy 70 abilities.