I would be fine with adding a way to indicate that an NPC can propose. As it is now, I sometimes make the NPC playable for that but I'd be fine with having this added. I also tend to do a lot of different things when they get engaged. Sometimes the woman asks; some households are more and less traditional. I mix up a lot of different ways for them to get married as well.
I think a wedding and romance theme has not been fully developed and is asking for a GP at least. I would like more customization and a lot more new romantic interactions so that it isn't all the same.
I'd like different themed types of weddings to choose, maybe with different budgets. Better wedding hair and veils. More interaction for the guests including any relatives. More details and ways to personalize the wedding. It should be easier to arrange the crowd of guests before the service. It has also been mentioned but slow dancing is missing.
I still have some that have quick weddings and others that have bigger ceremonies but this needs some work.