CO could have had a "Modern tank" with strong ranged firepower, mobility, extreme durability. But alas.
On the other hand for a mmorpg? Sure. Such a class could exist, we had close to it in CoX. The brute was very high in offense and could be boosted in durability very sharply. The class was the lightning bruiser. Lets not forget, modern tanks are very fast compared to older tanks to. Even going as far as doing a wheely. How to balance an mmorpg with such a class:
Screw the old trinity.
Go with "Muscle, support, control.", similar to GW2. A tank would be a "Muscle" class, capable of inflicting horrific damage and taking it simultaneously. It would be vulnerable to crowd control effects from control, but could be protected from that with support. Does something like this exist in games already? Yes, in RTS's. For example the starcraft series, such as SC2 and the protoss "Death ball" which comprised of, originally, Void Rays(The muscle) and support comprised of stalkers(who also acted as muscle) and collosus(the actual support) with the occasional high templar. Or maybe SC 1 and dragoons(muscle), zealots(both muscle and crowd control, they could body-block melee enemies to protect dragoons) and high templar. Or Terrans and marines/medics with science vessel support. Or even the ghost to disable dangerous mechanic units in SC1(crowd control) or a protoss arbiter/mothership disabling enemy units in SC 1 and 2 respectively.
Support units were often the units either repairing or protecting units with protection spells/powers, the crowd control effected enemy units and the "muscle" were units made to inflict a lot of damage.
Another game where you saw muscle/support/control was the command and conquer series. Often you had supporting abilities that helped with crowd control or protecting/supporting your own units, whether that was in the form of say bombers strategically used to protect your own forces from something nasty, or say an EMP to disable titan walkers ect.
Another CoH "tank" in a realistic mannor: Corruptors/defenders armed with time manipulation and force mastery could achieve very high defense ratings and high smash/lethal resistances, while having powerful ranged AoE. They were closer to being balanced from a weakness to defense debuffing.