Support specs would be a terrible step back in time. If you widened their abilities beyond the previous incarnation of Mana batteries and windfury totem chuckers then they would quickly unbalance the game.
Not to mention that playing a support class with the design of the game now would be completely unrewarding and not fun.
What they need to do is go back to designing encounters where people can step outside of their normal roles with the specs they have available. Think warlock tanking on Leo and Illidan. This is the reason why people say that TBC was so much better for raiding. We think those mechanics are outdated or not complicated, but they were used to the greatest effect. Now we have lots of varieties of stand in this spot, not that spot, watch out for this thing that falls from the sky, etc.
It would be pretty simple to give a dps spec a mechanic that heals the raid. There could be a fight where a tank gets linked to a dps, and then the dps needs to do very specific kinds of damage to a specific target in order to transfer that targets life to the tank. All other healing on the tank would be null. There are a million ways to do this and make people feel like heroes.
Just look at SSC-BT and you will see a variety of unique mechanics that actually made the raids challenging and fun. This is why people talk about raiding back then. It's not just nostalgia.