The new model gets an updated autofocus system.
There aren't a lot of updates to the X-E2S over the X-E2: they don't even merit a "What's new" section. Physically, there's a grippier patch on the grip, a slight aesthetic change to the buttons and an electronic shutter. In firmware Fujifilm has enabled the phase-detection sensors on the sensor, so it now essentially has the same autofocus system as the X-T1. That's good, since one of my gripes with the X-E2 was performance. Plus it now supports up to 1/32,000 sec with the electronic shutter and it has an updated user interface.
The good news is that existing X-E2 users will be able to get everything I mentioned after "firmware" in a free firmware update.
I admit to some bafflement. In June, Fujifilm launched the X-T10, which seems almost identical on the inside but different on the outside, and only costs about $100 more.
The X-E2S will arrive in February and cost the same as the X-E2: $700 for the body and $1,100 for the kit with the 18-55mmF2.8-4 lens. In the UK it will be £550 and £750, respectively; Australia will only get the kit, at AU$1,400.