I think a Sims 4 style building system would work best, as it presents a number of opportunities. It would be entirely optional, obviously, but imagine being able to build a restaurant or something and save it as a custom design to use again later. Placing tables and stuff would be no different to placing benches and lamps on paths. Floors specifically designed for indoor buildings, placing a kitchen unit with a front facing counter where people can order their food, maybe putting up a screen and some seats to make a rudimentary cinema area (that last one is a bit out there, but last time I was at Disneyland Paris, I took a break by sitting in an area usually reserved for stage shows, and they were screening old mickey mouse cartoons. It struck me as a great idea as a break for guests).
This is all hypothetical and I'm sure if it were implemented, Frontier would do a much better job of planning it out than I can, but it's something I've always loved the idea of in RCT and now that PC is a new take on theme park simulation, there's a possibility that this could become a "thing".