I think what'd been cooler is having the designer itself written in WPF, and not the 5-10 years old winforms list view. Karl Shiftlet has his new power toys, that show a more mature way to develop WPF applications, and the support you need when editing controls.
Don't get me wrong, the tried and tested stuff works, but WPF requires extra configuration that is missing in the old winforms designers.
I also don't feel excited about this as much as thinking, its about time that feature was available!
Also Milind, the Entity Framework seems to be the data access method of choice for WPF, will any work be done to allow the EF to be targeted design time by winforms applications?