Not high on my list, but if they added:
1. Slot games
2. Scratch ticket counter
3. Ring/cake/dress/wedding planner venue
4. Several cakes to buy there/make
5. Many dresses/men's attire
6. Wedding planner job
7. Variety of wedding rings
8. Garters-couple styles and colors
9. Podium to get married at(for churches)
10. More arches to marry at- angel columns arch
11. Perhaps a cruise get away as alternative to the casino.
12. Fiancee in CAS relationship choices
13. Riders for toddlers that might be stuck there waiting for adults to finish
14. Claw machines/arcade stand ups for kids for same reason
15. Heart bed Catloverplayer wanted
16. Engagement party to give gifts
17. Possibly connected hotel to rent/stay/run
Sounds like a bunch, but nearly all except the slot machines, job, garter, rider, claw machine, and running a hotel is already in game.
We already have rings, dresses, cakes, arches, podium(uni), beds, ceremonies ECT.
Hotels in Sims4 could use bunkbeds. More romance interactions. Bring back flower bouquets from Sims3 for ceremony and for giving. Express Love interaction always available for all Sims all the time. <3 Buy/give candy boxes and cards.