I think it was a mistake for Kate to move in. I think it would send a better message if she didn't move in cuz it portray more of a message that she was serious about getting married. Instead of doing the easier, more accessbile thing of moving in, she shoudl have had her own place. So if they do end up getting married, the element of surprise woudl still be there. Now w/ her moved in, it would not be surprising. It will be too expected.
That's why I kind of hope there will be another love for WIlls down the road. One that will not do teh easy thing and move in, but will be a pleasant surprise.