I figure they will get married at the end of this season, as TV Guide has hinted. It wouldn't surprise me if Castle put a deposit on the fabulous venue anyway, just in case Beckett changed her mind. He can afford it, plus with the waiting list, he wouldn't lose money on it if he had to cancel.
One thing I've got to say is that wedding gown is UGLY!! It's gray with gaudy crystal baubles all over it and the attached poofy skirt adds 20 pounds to her hips. Whose brilliant idea was it to deviate from the mode of all the other gowns she's worn on the show? They all were simple, elegant and classy with little if any adornment. I hope the ugly one accidently burns up or something so they can order a new, beautiful one. Kate is too gorgeous to get married in an ugly gown.