Sorry, but tanks are balanced right now. I don't understand why people want un-killable juggernauts.
In PvP, a Tank/Healer combo can already hold a node vs 4+ people for a long time. And as long as that tank had a healer in Huttball he would never die.
Sorry but it's balanced the way it is.
No need to be having tanks with 30K base health along with 2x their defenses they already have.