I am sorry, but this is painful. I made an account on this website just to contribute to this conversation. Sorry for the bump.
First, lets get the technicalities right. OpenGL is
NOT an engine. It is an API for rendering graphics. DirectX is also an API for rendering graphics. These two are the most common graphics APIs used today. You build game engines using these APIs. Example: The battlefield series uses the Frostbite engine, which rendered with DirectX. Unity3D can use either DirectX or OpenGL as the rendering method.
Gurren Lagann TSS and electricpants: Do some fact checking before abusing your caps lock and using pretty colors and formatting to gang up on Cesare. Taken from the wikipedia page of space engine: "The engine uses OpenGL as its graphical API and uses shaders written in GLSL." -
https://en.wikipedia.org/wiki/SpaceEngineSo yes, space engine does
NOT use any pre-existing engine, it is built from scratch... using
OpenGL.
So yes, Cesare was half-right, SE does use OpenGL, but OpenGL is not an engine, its an API.
Now, to answer your original question: Unity is an advanced engine nowadays, and you can definitely perform graphics updates on this game, given developers with enough time and money on their hands. You see, what you must understand is that it difficult to perform such a feat.
I very much identify with your feelings on the subject, I also wish for there to be very detailed planets and complex collision simulations, but even the current game is impressive in its scale. Adding all that will slow most PC's to a crawl and will need to be optimized very smartly to make it practical. Space engine was built from the ground up specifically to render beautiful environments. Universe Sandbox was built with the intentions of accurate physics simulations. Your demands are above and beyond the current technical and budget limitations of the team. If development continues, it may happen down the road.