Personally, I hope they never make another open world sims game. Open world is a wonderful thing for a game where you play just one character, or group of characters, like in an RPG, but for the Sims, it leads to having all of the sims 'active' even if they are households that you normally play, but rotate between. Just causes no end of headaches for rotational players.
On top of that, it takes all the resources to keep track of all those sims at the same time, leading to sacrifices in other aspects of the game and/or performance issues. Without really adding anything at all other than "no loading screens". I'm sorry, I'll take the loading screens in my Sims game in that case.
I would like to see them implement open neighborhoods though, where all lots in one neighborhood are loaded when you have a sim there. And add seemless loading, rather than loading screens. Which is actually what games like Skyrim and World of Warcraft do. They have the appearance of being "open world" but the world is actually in grids, and only the grids closest to the player are loaded at any given time. The loading happens in the background as you move about, so you don't see loading screens.