via the Dude over on Warseer pt 1
More info is coming to light regarding the Tau release. What I've personally heard is:
*Aun'shi is rumoured to be returning.
*Two new characters are said to be included.
*One character is a tank commander (presumably a vehicle upgrade) like Pask from the IG Codex. He is supposedly in a Hammerhead and allows it to overwatch.
*The other Character allows Fire Warriors to consolidate after Overwatch.
*So it seems Overwatch is going to be the Tau's special trick, at least from a Fire Warrior perspective.
*The large suit thats been rumoured for a while is supposedly called the Riptide. It is a Jump Monstrous Creature armed with Ion Cannon and standard Battlesuit support weapons.
*The Ion Cannon can reportedly use two fire modes, Heavy 3 (possibly 4) and single shot Large Blast.

I have heard of the following releases:
*Riptide large suit
*Flyer dual kit (fighter and bomber)
*New Battlesuit and Broadside models (not sure if these dual kit or not)
*Plastic Pathfinders
*A new Fire Warrior HQ (not sure if the special character mentioned above or a generic one)

via the Dude pt 2
*Ethereals buff units that they join with a selection of effects. One such effect gives an extra shot. This combined with a piece of wargear that adds 6" max range to the squad means that it's possible to rapid fire 3 shots at 18".
*Apparently this can potentially be 4 if the Fire Warrior special character is also attached.
*Riptide is rumoured to be around 165 base but only start with twin-linked Plasma.
*The Ion Accelerator is apparently an upgrade: three S7 AP3 shots or one S8 AP2 Large Blast.

*There's supposedly a special rule on the Riptide called Nova Accelerator which can do 4 things:
Buff weaponry (unsure how or which weapons)
Double the shots of support weapons (missile pods ect)
Increase invulnerable save to 3++
Boost a stat (unknown which or by how much)