From what I've read, the new XP3 isn't designed to "replace" the Failsafe (contrary to some here, I like it a lot...it isn't a benchrest bullet, but boy will it sure plow through a Moose!) it is designed for DEER sized animals, while offering Failsafe performance with greater expansion.
The problem Winchester was encountering was guys buying the Failsafe and using it on a 150lb deer at 40 yards. The Failsafe would punch straight through the deer and hardly expand. It was designed for use on big bodied Canadian deer, elk, and moose out at least 150+ yards.
So basically, the XP3 bullet is designed to offer Failsafe performance at closer ranges, slower velocities and on more thinly skinned game. The biggest difference from the Failsafe is that they lost the steel cup and have gone with a process similar to the Accubond. Manufacturing should be easier, as a result, and it will probably be easier to create more uniform bullets which should translate into a more accurate bullet. Time will tell I guess.