I dont think they are done. After shatterd space they probably want the next dlc to be well received. I doubt many folks are still working on it and it will take time.
Everyone says they want ES6. They are (hopefully) all hands on deck for that. If they hadn't done starfield then ES6 would be the first game with the new engine. That would have been a disaster.
I expect the next dlc will be the last for starfield. Thats ok. I personally love the game. It's huge. It's unique. It is very Bethesda.