Here’s a strange idea, I somehow doubt it’s even technically feasible.
Imagine a large space station of sorts that is surrounded by a huge expanse of eeroe, possibly glowing fog. The fog is generated and contained (prevented from dispersing too far) by the station using science and technobabble. In essence it would be like an artificial “space opera nebula”.
The purpose of this fog would be to visually and electronically conceal what exactly is going on within it, like secret projects and stuff.
Gameplay-wise this could create a pretty interesting environment. Inside the fog your sensors would be disrupted, and your visibility limited. You might even be subjected to atmospheric conditions.
When fighting in this place you’d have to keep your allies close or risk losing them in the fog. The lack of visibility would force a slower approach, closer engagement distances, and enable hit and run tactics.
So yeah, that’s the idea. I guess you could also/alternatively have bases in gas giants that would create a similar scenario.