Games Workshop is still swinging out the bait for us to much on, and believe me, im munching on it.
This time around its changes to the Battle Focus Rule.
As you can see the previous ability to fire assault weapons without suffering the -1 to hit is still in here, but it's the second ability many are saying is broken.
Don't get me wrong, I remember when Tau came out and the "Assault Jet Pack" became a thing, with them flying back and forth out of, then behind LOS blocking area terrain, but before that, Eldar could have a Crystal Targeting Matrix on Second Edition Eldar vehicles which allowed them to part move, fire, then part move again (As always Tau players, Eldar did it FIRST).
I can see Dark Reaper units moving a couple of inches into Area Terrain, shooting, then making sure that roll gets them out of harm's way. But what if you fudge it? what if you roll low? For me this rule isn't broken, it adds flavour and character to an army that was once the fastest on the battlefield and Guaranteed when I'm playing I'm rolling a 1 and that unit is pretty much stuck.
We will see what effect this has on the tabletop when folks start playing, we haven't seen much in the way of points cost for Eldar just yet...They could be really expansive to field and you may NEED this rule to keep the glass cannon alive as long as possible.