Now if, back in 1978, you'd told me that there were going to be three main character classes in future MMOs, I would probably have assumed some kind of rock/paper/scissors relationship among them for reasons of balance. Archers beat infantry, cavalry beat archers, infantry beat cavalry — that sort of thing. I don't believe for a moment I'd have gone with what we have, which is the "trinity" of tank, heals and dps....He goes on to explain that the "tank" role came from MUDs (early online RPGs) that lacked positional systems. Everyone was either in a room, or not in the room. Therefore, there was a need for aggro management: ergo, the tank.
D&D has traditionally handled this as wargames do, with pathfinding or keeping track of locations. This requires greater granularity and fidelity, though, in that you need to track locations of pieces, usually with minis. It also starts to break down in some scenarios.
I am reminded of G2, Gary Gygax's module about frost giants. Maybe I am a huge jerk, but as DM I used a lot of missile fire (as the dungeon key suggests) from the giants, and I played the ogre magi to their maximum potential. Heavy missile fire which can essentially ignore the strong "front line" tanks and the threat of flying invisible ogre magi with AOE spells like Cone of Frost made some sort of "taunt" ability necessary. The player running a paladin role played this to the hilt and sought out a magic sword with the "Taunt" spell built in. The other fighter went with the "whack giants with a two handed sword dealing 3d6 damage" route so they had to pay attention to him.
The point is that if the system allows enemies to ignore the tank for some reason then we're back in the early-MUD DPS-Tank-Healer trinity conundrum again.