I have not miss the upgrade part... planetory module will be the upgrade part... planet is the basic starbase, planet module will be option added to it...it will give the impression that the station grow with each new option...
You will say that module cannot be in contact with the planetstarbase because the are in collision box and the engine don't allow it... it is where the particule effect is coming... it is particule effect who link the planet module to the planetstarbase... particule effect are not stopped by the collission box...a simple tunnel/conduct from the planet mesh to outside the planet box will be enough... will be more easy that the reverse since planet are perfectly centered on any axes...
Maybe one problem... have not yet think about it... planet rotate... if we cannot stop the rotation, everything will be misluck since the particule effect will rotate with the planet...
Other case, about a ring, you can create one around a planet but from test and trial, you need minimum 3 pieces identical... and it will work only around planet who have all the same inner gravity wheel... around asteroid, it not work... and gravity wheel will be to much little... and no AI player allowed, will explain why later...the 3 basic part will be the same mesh, with always oriented to the planet set in the entity file, they will be one cheap planetory module without any function, only for the eyes... the other planetory module will be options...
For mister "impossible" some picture who illustrate the principle...
First section :

Second section :

Last section :

Now, the theorie :

blue box are the mesh box... red ring is the inner limit of the planet gravity wheel ( identic for all planet, different for asteroid, for sun, pirate base and gas giant )
Yellow part are place where the mesh need to be change... yellow part need to be some connection ( simple cylinder is good )... box 6a, 6b, 6c are planetary module... need to recreate all the mesh of module, so they will have the same box and will connect perfectly to the basic station...
Why the project was stopped... modeling is really difficult and complex trigonometric calculation are needed for the mesh part will will be in contact... mesh size need to be calculated too in function of the inner ring... position of the piece is in someway difficult... but mainly, the AI screw everything... he build basic part of the ring everywhere and not near the planet... result is ugly for AI player and it slow down my fleet when i try to attack them ( need to go around all the piece ) and capital are very slow for rotate... my ship don't attack the piece since they have no value and since i have give them 100k hull !!!
So, the engine itself will allow you to make a lot of think... 1.05 was good enough for it... AI is the real problem... you cannot predict how they will react and how they will use new thing in game... Similar problem was existing with the ship graveyard... with AI putting a lot of ship there who was just sitting and waiting... AI have act like the derelic ship was a danger but was not fighting... or sending a colony ship to capture the derelict ship...
Since the AI cannot be modded, it is a dead end... you can only use what is implement by Stardock... It is why so much people complain about the Entrenchment... AI spam mine... not a big problem, stardock will tune the AI and change the behaviour... screw the gameplay for a ring is not really important...
People, believe me... the sins engine can allow you to make a lot of thing if you have the needed imagination... by example, there is 1.05 mod with starbase... or the B5 ship with rotating piece using the particule system... engine is not a big problem ( unless your reach his harcoded limit ) but the AI and gameplay is a real problem... gameplay can be tuned with entity file but AI is out of our reach... no rules file that we can tune...