[GC3 is a great achievement, even as it stands now at v1.11. That said, the forum section title is "Future ideas," so I'll bury Caesar now.]
The map features as they exist now are not especially interesting; you basically have places you go, and all the nebulae, features, and cloud types which are avoided barring a handful of rare tactical reasons for entering them.
I think these might be low-hanging fruit:
-Cloud LOS delta: no matter your sensor range, nebulae hexes of [insert selected types here] block LOS. This would allow ships to hide inside nebulae, and create frustrating situations when a cloud functions as part of your border. (What are the Thalans doing over there? Should I send a ship to check?)
-Black hole speed delta: you can't fly next to the black hole features, but going anywhere near them should slow down your ships, with an increasing effect by proximity, to the point that ships below a certain speed would be captured and immobilized in the nearest navigable hexes, as they utilize all their thrust just staying out of the event horizon.
-By that same token, we could introduce some "slingshot" effect when ships navigate next to stars, adding an additional move when starting/ending their turn adjacent to a star.
Those are the basics. Apologies if someone's already posted these ideas. Best of luck.
KOU