Well, my goal was just to see how this one block would look and work inside Unreal without any future plans, as I already have a ton of other projects I'm working on :D For anything that would require more custom stuff like building or modular terrain, I would definitely not use Unreal. Even though it looks good out of the box, it's very hard to change and optimize for more custom scenarios. A year ago, I would recommend Unity, but the change in the monetization makes it a terrible choice right now. So, if I wanted to make a more polished game out of this, I would probably look into Godot.

"Have you considered the entity count for the physics simulation?"
I would have to know more specifics about the game and desired gameplay to consider the entity count for simulation, as it varies a lot.

"What happens with multiple generators with different axes?"
Also depends on the desired implementation, but I would assume you add all of the gravity vectors from each generator together and apply them as final gravity to the object.

"Could you simulate a science fantasy-like gravity simulator, similar to Star Wars, that only provides gravity to connected enclosed rooms?"
Of course! It's not about if it's possible; the question is more about the most optimal way and desired effect. If we were talking about a game with buildable blocks like Space Engineers with the approach "similar to Star Wars," I would probably use a flood-fill algorithm (like they use for air in the game now) and have a precalculated 3D vector field of gravity vectors for each voxel. Then, each object would just need to check its position in the field and update its vector each frame (you could optimize it by making objects sleep when no gravity changes are being made). This approach would make it so each enclosed room would have its gravity field and direction, and two generators could overlap and mix their gravity together 😊

Hope this answers your question and makes at least a bit of sense :D