Tankasin and Shadow Tanking
"The Sith Assassin's tank spec is more of an avoidance type in PvP. You'll end up blocking, dodging, and that kind of stuff as opposed to having natural mitigation within your armor like a Bounty Hunter or a Trooper Vanguard."
The above statement has led to some speculation about the Assassin/Shadow's tanking focus.
The general belief by some members of the SWTOR community is that Tankasins and Shadows are avoidance tanks. Warriors/Guardians and Troopers/Bounty Hunters are heavy armor tanks, with a large focus on mitigation. Avoidance tanks, unfortunately, have a bad reputation amongst the larger MMO community. With that in mind we've seen plenty of indications that Tankasins will close the armour gap through active abilities and buffs.
From what we've observed it seems likely that Assassins and Shadows will use a combination of avoidance and mitigation. They're not an evasion tank in the truest sense, and that's a good thing. Increased chances to shield, increased defense, buffed armor and endurance and the ability to debuff their enemies certainly moves Assassins and Shadows firmly away from being pure avoidance tanks.
The common query on the SWTOR forums is this; are Assassins and Shadows viable as Main Tanks? This site exists to answer that question... YES!