Balanced

Heckler: "And just what can you do?"
Mako: "I can talk to fish."
Heckler: "Haha!"
Mako: "...and eat people who laugh at me for it."
Heckler: "Uh-oh."

Interesting notion. At this point, I'm willing to at least consider almost any reasonable alternative to the current Vigilance.

Tracking attacks directed at the team might be more trouble than it's worth, really--they could keep the current "team health" model (modified to include the defender!). As the team health drops, the chance of triggering a proc on each attack increases. The proc would probably be a broad-spectrum protective debuff (to-hit, damage, recharge, and maybe -mez magnitude/duration) that would substantially reduce the damage from affected mobs (as opposed to making the mobs easier to kill).

It would be harder to exploit than Defiance. It's unlikely that you could persuade a whole team to stay in the red just to get a better shot at protective debuffs; it just wouldn't make sense. A solo defender wouldn't gain much by gaming it, either--it wouldn't make kills any quicker, so it would just leave the already squishy defender at critical health for extended stretches of combat. The improved protection wouldn't really offset the increased risk that well; a lucky shot from a mob or a failure of the proc could spell defeat.

It would also encourage more balanced defender builds, because it would provide a new reason to take and use secondary powers. I like that, personally, but you'd probably hear howls from so-called "pure" defenders who are still afraid of drawing aggro.

Thematically, I'm not sure it would still fit the name "Vigilance", I don't think. I'm not sure what you'd call it. "Intervention"? "When the Defender's allies are vulnerable, he leaps into action, harrying and distracting their foes, buying time for his team to recover."

You could just skip the check, and have it apply to everyone on the defender's team. We're everywhere, you know.

Perhaps they will eventually be able to use the alternate animation tech to make this possible, by adding an animation that doesn't do the model replacement. What I'd really like to see would be a version that replaces all textures on the PC model with a tintable granite texture, so that it looks like the character's skin and gear was turned to stone--the character as a moving statue.

Yes, you can select animations and colors on each individual power. Furthermore, you can select different power tweaks on different costumes. You could even make two identical costumes with different animations and swap costumes occasionally so that your character uses all of the options.

The Reveal power is a vet reward, not a booster power. The "power" for the booster was access to model changes at the tailor.

Paranormal heteropaternal superfecundation, for one thing. Does that help?

My very first use of the booster was on a Magic character. Part of the character's backstory is that a pair of fraternal twins (a boy and a girl) are stuck sharing the body. Since the boy was the healer who created the merged form, it was male, much to the girl's frustration. Now when it's her turn to run things, she uses magic to turn the body into a girl. (Well, a demonic female form, anyway. The boy gets the angelic male form. It's a weird family.)