Mind control is currently pretty useless.
In PVP it just takes you and the person you're fighting out of the fight for a few seconds. You don't gain their abilities so you can't really do anything.
In PVE its very situational. If for some reason mobs are too tough to AoE they are of course immune to MC. Even if something can be MC'd its never safe because MC breaks as soon as you take aoe damage and then it comes after you. And don't forget the MC'd mob always does lower dps than you anyway so you're all around better off using any other classes CC. Then there's also the aggro bug. If a tank pulls a group but doesn't actually do damage to all of them and then I start casting MC I gain aggro of all the mobs the tank didn't actually hit. This doesn't happen when I finish casting MC, it happens when I START casting it. Many people don't even know about this very frequent bug because, frankly, no one uses MC enough to notice it.
1. MC works like madness. You cast it and the mob/player acts as if they're under the insanity debuff on yogg. They cast random stuff at random allies. This would allow you to retain control of your character and not have MC break on damage all the time. Lasts 10 seconds. 30 second CD.
2. MC doesn't break on damage. This would at least make it no longer be horribly reckless and unreliable.
Part of the problem with buffing MC is that disc priests dont need any buffs in pvp and I'm approaching this from a shadow pve perspective. Maybe insanity should just be a new ability in the shadow tree? Shadow needs pve and pvp buffs doesn't it?