@ikkyg in recent discussions about spiral staircases an EA Community Manager informed us that he has raised the request for spiral staircases directly. So it's one we've been hoping for and it's great that the feedback has been passed on. Fingers crossed we see it in the future. I'd like the style I've seen in Sims Freeplay. But for now I use a single tile width staircase and twist it, it's most effective using a tall wall height. I usually leave off the railings as they can make it look a little cumbersome. Luckily Sims can't fall downstairs! I also find it looks better with the metallic stairs in the game, depending on what packs you own. The marble looks good too.
I've placed elevators too but they can't obviously be used as an elevator in a regular home, it's just decorative or used to travel and you still need to have a staircase. There are YouTube tutorials on the subject. Added an image of one from City Living.
I'd like a slide as I have a water park and it could really use a slide.
You can make a grand ballroom staircase already though. I make double ones with 2 adjoining staircases and single ones with one wide one. I find that the marble from Get famous works well but the High school years stairs work well too. You just need to widen them and use a fancy railing and matching fence. The Get famous ones again work well but so do the Realm of Magic ones for me. I'd like to see more carpeted ones though because I think that would look better. As @jpkarlsen they don't have a railing through the middle. I'm not sure why that would happen but you could add an image to show us what you are seeing.