For starters, their damage and survivability will move closer together. We want the decision to be more about utility of their abilities than dps or squishiness. Under the new scaling model, the Imp and Succubus have health, mana and armor not too far off from the Felhunter.
We tried out the Imp doing friendly damage when he dispelled because we thought it was interesting for the demonic feel, but we have already removed it. We also tried an ability to knock allies out of CC that break on damage, but we now think that would be too powerful. Currently the Imp still does a dispel on allies.
We wanted to split Devour Magic into offensive and defensive components or else we felt like the Felhunter would always be the obvious choice for PvP. Now you can choose between having an off-the-GCD silence / interrupt and an offensive dispel / purge -or- having a defensive dispel, increases health and an escape tool.
Like everything else in beta, these are subject to change. We're close to being able to get more max-level PvP feedback and will buff or nerf abilities accordingly.
imp wont be able to break blind anymore (