What people are missing is that they didn't have to ditch 'open world' in order to reduce loading issues. I appreciate that they removed it to make the game run better, but I just think that was taking the easy way out as opposed to actually fixing the technical problems.
Take an open world RPG, like Two Worlds or Skyrim, or even much older Oblivion (I'm choosing this genre and these titles purely for examples). You didn't have loading screens out while running around in the wilderness (only when passing between two completely separated world spaces). That is because the computer only loaded your active cell and the ones directly around it at any given time.
Multiple games have already perfected ways of tracking and dealing with NPCs and other entities that are not currently in the loaded cells. Some of these games have hundreds of entities with more AI and activity than what's being showcased and discussed in Sims 4, with little lag. Heck, I've seen text-based MUDs handle this issue better than what I expect to find in the Sims 4 (and most of those games were made in the 80's and 90's). So far, the only thing it seems off-camera Sims are capable of doing is age and die.
The world lag in Sims 3 was due to multiple issues, including trying to render lots VERY quickly (cuz players could pan fast), track everything through Story Progress, pre-loading the hundreds of objects added by purchases, Expansions, and Stuff Packs, load all meshes and textures from CAST, etc. etc. But ALL of these features have been cut now, and for all the bluster about optimizing the game, it's still running single-threaded and 32-bit, for reasons that I can only imagine are related to engine licensing or some EA executive who had no understanding of computers calling the shots early on. For our purposes, this means that the game is not future-proof, and will eventually become as jacked up as the Sims 3 was when you get done adding 3 or 4 more expansion packs on top of it. It also means that modders can't go hog-wild with creations (like they've done with Sims 3, creating MASSIVE, feature-packed worlds), because right from the get-go, you have PHYSICAL limitations as to what the game can do.
