If that really is what the mk8 will be, it will be the smallest design change since the mk2 (and maybe even including). Unless it has a lot more than just design changes I don't think that would have the right to call itself a mk8 rather than a mk7.5 v2. The biggest change I can see other than the grill is they moved the crease down the side of the car up to the door handle, and did some minor detail tweaks. I'm very skeptical that they would choose such subtle design changes for something as important as an entirely new generation car.
I believe that the MK8 is less of an entirely new car than the MK7 was.
The MK6 was an improved MK5.
The MK7 was the big change, with the switch to the new MQB platform.
So, aside from increased power and features, the MK8 may share the same body as the MK7.
Generally, when a car is refreshed - like the MK7.5 is - we get a glimpse of the styling of the next gen. car.