For sure. Or offer "Vanilla" servers. I remember back in the day Ultima Online servers would pop up form time to time with the classic UI.
In that expansion I'm sure you're talking about, paladins are somewhat better, and shamans are worse. That's normal, and it's not a problem when you play in live servers, since they are making modifications to spells and everything constantly. But when you're stuck in some version, then, you're stuck with how classes work in that version forever. That makes the population lean towards one class.
More information about FOTM here: http://wowpedia.org/Fotm