Each removable battery and motor weighs over 110g and must be mounted to the seatstay or bottom of the downtube by two zip ties. It will be very difficult to get a firm and reliable fit because frames use wide range of shapes and sizes. With each shift, there will be a lot of pressure on the battery/motor assembly to shift out of position. Rough roads or technical singletracks will also knock the Xshifter out of alignment. Once this happens, you'll probably have to replace the zip ties and dial-in the indexing. Not exactly fun in the middle of a long ride or while touring. It doesn't help that the seatstay and downtube are exposed to a lot of moisture and dirt. Maybe this is why the demo was done on a Shimano Acera 8 or 9 sp derailleur, rather than a 10 or 11sp drivetrain.
It should be noted that the biggest advantage of Di2, eTap, EPS is the fast and reliable front shifting. These systems are very reliable because the front derailleur moves quickly and intentionally over-shoot, but retract slightly to keep the chain on the right ring. The Xshifter can't do this.
The Xshifter also only works on half of the shifts, when downshifting to a larger rear cog, or upshifting to a larger chainring.