The Project Rene/Sims 5 announcement came long before they were ready to actually make it, because their hand was forced by leaks. It's going to be a few years yet. And in the meantime, they definitely want to keep making sales, so count on lots more content being released.
Now, what will be in them? I think they've addressed most of the big wish list items we've been begging for since forever: Farming, meaningful baby interactions, stuff to do as teens, werewolves, horses. The only item I can think of that they still haven't given us is cars. And, what would cars look like in TS4? A glorified travel animation? Everyone gets in, it reverses out the driveway, and then the loading screen? So, I think they'll get back to surprising us. Let's hope the surprises aren't of the out-in-left-field variety like the Star Wars pack.