You don't need the trinity in PVE. You just design your mobs and encounters around other teamwork concepts.
The greatest barrier is getting people to be willing to learn a new system of organized PVE. A lot of people could not adjust to GW2 and just gave up quickly. I believe EQN is ditching the common trinity as well. The hardest job for each dev that tries this is to introduce new concepts and get people to observe, learn and value them.
There's nothing particularly more tactical about the trinity. In fact, I feel WoW began reusing fight ideas years ago and the encounters started to get stale. You can do new things and new ideas without the trinity. It's really just a matter of encounter design and getting people to open up their minds.