Yes, they have one ZI 28mm on display the other day I was there. If you talk nicely or make the lady feel that you know this stuff well and not likely to damage the lens, she might allow you to try and hold it (she said I could bring my Leica and try if I am seriously keen. fair enough.).
I used to have the G-series 28mm lens and it is a superb lens. If this ZI one is as good, it would be a winner. However, from the published MTF curves, the G-series appears to be superior, in terms of sharpness/contrast and distortion. I have not come across any review/comparison of this lens vs the summicron yet.
While I understand that ZI lenses are supposed to be Zeiss' design, the actual look and feel of the lens is clearly that of a typical VC signature (the finishing, the colour of marking, the filter mount, the weight...come on, it's just world apart from my Zeiss Biogon 21/4.5 lens for Contax S-series RF.) While I have no doubt these ZI lenses would be very good performers, is it worth paying 2/3 Leica price for them is another question. (for Leica, you pay for both performance and "siok" factor, IMHO, YMMV)
Shalom!