As far as nerfs go, they kinda already did that by taking away formations. Triptide Wing, OSC, Piranha Firestream, Drone Net, pre-FAQ Hunter Cadre, that's the stuff that made us super cheesy. Take that away and I think we're average.
One thing I'd love to see is Tau armor that's worth fielding. Based on the profile for the Leman Russ main cannon, I think we can safely anticipate that the heavy rail cannon on a Hammerhead will be d6 damage and a single shot, with AP -4. That still feels a little underpowered compared to the LR though, what with it's d6 hits and d3 wounds. I think they'll probably give it the melta half range rule to boost it. I'm also interested in seeing how our armor compares to other factions. I always thought that we were sort of a halfway faction between IG and Eldar, in that our vehicles could move and shoot, but not move too fast. I'm thinking our vehicles will all be able to move and shoot heavy weapons without any negative modifiers, and our performance will hold up better after being damaged.
In any event, I'm super stoked for 8th.