Besides Arc weapons for the Skitarii, rumors are talking about new exotic weapons from the Adeptus Machanicus. New Burst pistols, Cognis Weapons, and Galvanic Rifles which may be the standard weapon for some units.
Please remember that these are rumors. Please take with salt.
via an anonymous source
here are some rules for some of the guns for the ad mech. I dont recall seeing much more.
Cognis Weapons are normal weapons with the Cognis attached to it, like Cognis Lascannon. They simply use a BS 2 when firing snap shots because of an awakened machine spirit.
Burst Pistol rules allow for 5 shots to be fired instead of just a single one.
Galvanic Rifle looks like an ornate flintlock rifle with a canister on the side. R30", rapid fire, S4.