The trinity, in its current form, leave no expansion on roles other thank EHP, DPS, and HPS. Sure you can get even more specific like Avoidance tank vs Mitigation tank, Range vs Melee and Single target vs AE, but these roles still have one common goal.
There is no more controlling the encounter from anyone, bar mechanics and tanks. There is no more pulling, just taunt.
There can still be really cool role designs, just nobody has the balls to go there.
GW2 was on the right track, but that game was designed for PvP, and not PvE. The roles were never defined, and such never really balanced for PvE either.
Here are a few ideas of some roles I could see being a ton of fun.
Support (Controller) - These people control fights. They knock down enemies, blind them, confuse them, all around beat their senses.
Puller - These people also control fights, mainly the beginning are important in how they setup the pull. They could lay traps, devise routes, and are really good kiters.
Bosses are no longer 'fixated' on tanks through threat alone. It is the job of the support and a tank to keep the boss focused on him. Tanks would have more abilities to jump in front of bosses and save team mates.
I mean there are so many things that could be done to break up the trinity, but I haven't seen a well implemented one yet.