In the mid 2010s I worked on a social game and everything looked like it could be a social game. Managing a cafe, a hotel, a pet shop, a hot dog stand, etc. You had an idea, it could probably be turned into a social game.
While it was all the rage I thought: “Hey! There is a lot of planning going into a wedding; it could probably be made in a game”. A game could be built around dating from meeting your significant other to the big days which there are some games already doing that.
However, a game about planning weddings should be about the wedding planner since the average bride and groom will probably only have one wedding. An argument could be made that a game around a venue owner could be made, but that would look a lot like a hotel manager, which already exists.
Some game play idea
This game could have two modes: a story one and an online infinite one. The gameplay is similar between modes. The main difference is that the clients are scripted in the story mode and in the online mode you can share client and contact.
The main game play is to find clients and make them visit contacts and venues. You meet the clients and they tell you what they want for what budget and you try to bring it to them. You then go around and shop for them, calling venues, calling your contact to find the right photographer, videographer, florist, etc. You can then strike a deals with them. You then book the couple to meet all these amazing people.
As the game progresses you get more clients and you manage your business. You could probably use your money to buy traditional social game items like decoration for your office, perks like an assistant to make more calls, etc.
Then each client has their wedding ceremony that you can assist, in the story mode there could be some event that you need to fix (the wrong flower were given, the cake is not on time because the baker’s truck broke down, etc)
To have flavor each client has their personality and not all couples will make it to the wedding. We could draw some inspiration from wedding reality shows here to find some crazy scenarios played out. We could probably have a puzzle or roleplay between each step toward the big day.
The basics could be ads and cross promotion with another game. Sprinkle some items you can buy for your office and a special currency to speed up the process to the key point of the wedding. If you include some puzzle in between we could have them use the external currency when they fail the puzzle to retry or continue (like Candy Crush Saga). There could be special limited time events each month or week where there is an unexpected couple that wants to get married and you have to fix them up.
Hope it gives you an idea to build the next big free to play game or at least give you ideas for other projects.