This seems like a good concept for an SP or as a part of a broader romance pack. I agree with most of what has already been said. I'd want decor for more types of weddings. If they really want, they could add a wedding planner feature or something. There could be more cakes, signature cocktails, more possible themes. More dress, veil and tux options could accompany the different themes.
Examples of themes? Extremely formal or "princess-style", rustic (I know there's a different wedding arch for that already), casual/backyard/budget, beach, modern, updated traditional, etc. Yeah, I know that you can put a wedding basically anywhere now but weddings are pretty generic and basic.
I'm not obsessed with weddings but with a rotation, there are a lot of them in my game so I'd like them to be more customizable, less formulaic and less boring. They could add some "generations" moments with emotional speeches and more teary eyes. I like the idea of gifts or even a shower/bachelor/bachelorette party. They could bring back the champagne toast if that hasn't already come back.
I agree about the return of slow-dancing. Kids at a wedding could have their own goofy interactions like their own funny dances. I don't know, I liked Generations. I'd make it a way to bring all the ages together.