There's going to be a reputation system in 2.1 that allows players to +rep those who were helpful or pleasant when they finish an instance together. Supposedly there will be special rewards for us to spend this on so what you're asking for is basically already coming.

IMO another good fix for this would be to introduce a random DF queue that basically puts you into any instance in the game that other people are queuing for and gives you a special bonus reward for doing so. WoW and Rift both had this and it was very effective at ensuring there was always someone willing to run content with you if there was a specific (and otherwise less popular) instance you needed to run for one reason or another. The level sync system is perfect here as the random queue can literally cover everything... it would make those long queues for lower level instances a thing of the past.