The positioning system on most FDM printers is “open loop”. The stepper motors are told to step and the printer just assumes the steppers actually get the printhead to where it’s supposed to go. But there are many sources of error in the positioning system. When those error sources are large enough, you get visible artifacts on the outer wall or in the worst case, an outright layer shift.
Servos won’t have either of those problems.
The positioning system tells the printhead to move, encoders on the mechanics provide feedback to the positioning system. So with servos, the positional repeatability is much, much better. Servos can also generally operate at higher speeds because they directly monitor and control both position and velocity of the motion system. The motors aren’t steppers and that allows a much higher level of control.
There are a lot of ways to make encoders. There could be something inside the rail. All those screws suggest it’s a two-part design. But a shaft encoder in the printhead, driven by a pinion that rides on the rail might be another possibility. And they could do it with an array of alternating polarity magnets on the back of the rail, and a Hall sensor in the printhead.
I’m just speculating, of course. But Servo control would be a significant enhancement of the motion system. The new printer appears to be about the same size as an X1C, but more expensive. Encoders and servo control costs more to implement than steppers. That and the printhead itself could account for most of the additional cost.