Star Wars: The Old Republic finishes up its series examining the class changes coming with the 3.0 update today with the Sniper and the Gunslinger. Why were those two the last on the list? Probably because they were hiding way in the back. That's sort of how they do things. As both of the base classes (Smuggler and Imperial Agent) have seen some significant changes, some of the changes to Snipers and Gunslingers focus around keeping the core utility of the advanced classes while removing unnecessary or superfluous buttons.
Sharpshooter/Marksmanship are fairly unchanged from their current incarnations, save for a new ability replacing an older ability in regular rotation. Engineer/Saboteur is largely unchained, but the changes to abilities should produce smoother overall rotations. Last but not least, Virulence/Dirty Fighting specialties both gain a new ability that functionally replaces an older option and a new passive ability to spread damage over time. Check out the details on the new tricks on the official development blog.