Pally will always be the better main tank for any boss encounter, its mitigation is far superior to that of a warrior. That being said yes a warrior could be a main tank but only if your party really loves to rotate mitigation skills, but warrior is far better built to handle adds, since it can generate hate on an aoe level, its skills absorb massive amounts of hp and let us not forget it generates way more dps while in defiance(even single target) than a pally can even pull off in sword oath.
2.1 will not change the 2 tanks roles, but it will make players consider warrior a viable option for off tanking in any dungeon, since most players now rather run 2 paladins than 1 war/1 pal.

Side note: DPS marauder is a viable dps/tank for mid range encounters and waiting for an allagan axe to drop(once we beat T5) for our coil group to test if indeed a marauder could tank higher level boss encounters.