Illum, don't need to use caplocks. YOu can your words to make them emphasized.
But, it appears that those who've set up in one camp aren't really going to change their mind.
But, in D&D, you can't make Called Shots because it's believed that *everyone* is trying to hit the vital areas.
However, Rogues hit even better. They know how to twist the blade and jerk it just right; something that is still doable when you're raging. Furthermore, it hurts *worse* because the Barbarian/rogue is raging. Think of the rogue stabbing his knife into someone's side, and twisting, before pulling it free. The Barbarian would punch harder, Jerk it upward, and *Yank* it out with more force, ergo the extended strenght modifer.
I don't see any Unbalancing factor about allowing a barbarian/rogue sneak attacking. What are you trying to prevent them from doing? They have to decide if they want to rage, or sneak attack, in combat, then. So it's either use One class, or use another, in classes that are combat oriented.
How can raging effect sneak attack? Let's say the two are flanking. The enemy turns to deal with the fighter, and the angry rogue slams his axe into the enemy's back, and yanks it down. Hitting someoen in the back or the neck or a limb, or other vital areas, doesn't take much concentration; it just takes the same amount of time as a regular hit.
All rogues have to do is Hit someone, when a sneak attack applies. No taking an extra amount of time to concentrate, no focusing. I have to agree with Illum since it's the Person who looses their dex bonus, that opens themselves up to get hit, not the rogue doing anything special to their attack except hitting them. The *Flavor Text* is what says rogues hit vital areas.
Edit: Furtheremore on Concentrating and taking time, let's look at the skills that are void when Raging.
Move silently. You can't Run when you're moving silently, you can only move half your movement rate. That means it takes more time then moving regularly. That takes concentration, when raging.
Casting a spell. That would generally open you up to an AoO if you did it in combat. It's leaving you open, and unguarded, focusing on the spell itself.
Craft. You have to take hours or times to work on this. Can't do this when you're pretty angry.
Intuit Direction. You're focusing on figuring where you're going, not really strong and angry tryign to hit things.
When you're sneak attacking, you're trying to hit things very effectively. When you're raging, you're trying to hit things harder. Why can't they go together?