Some tests of the Xi3 have started to show up online (NAF) and in print (CR), and my impression so far is that the Xi3 is not much of an improvement over the Xi2. It has lower rolling resistance, and that is about it. Its dry and wet handling is a little worse, even though its speed rating has been bumped up to "H". Most of the listed sizes of the Xi3 have an XL load rating, which will not help ride quality. And the Xi3 has apparently not improved on the Xi2's relatively poor lateral traction on ice.
I'm not sure why Michelin has bumped up the speed rating to H (130 mph). Usually, that rating is only found on performance winters, and not on "ice&snow" tires. It seems to have paid for this speed upgrade with reduced ice traction, compared to the competition. In last year's NAF tests, the Xi2 blew away the WS70 and HakkaR on the ice braking test, but this year the Xi3 comes in second to the WS70.
TireRack should be releasing their winter test results soon, so we will see what their verdict is on the Xi3.