I don't much care for PoBs so I stay clear of them, a pretty simple solution.
However it seems by the comments on this thread that the two main issues are Base position and strength. What if each system had a number of preset locations say near jumpholes, off the side of tradelanes and in fields. For example illegal groups could build near jumpholes and in fields where as lawful groups could build off tradelanes and near jumpholes creating a contested area. Obviously the two can still attack each others bases, they simply can't build on those spots.
To balance the bases using the core upgrades have it limited, illegals can build up to level 3 in fields but only level 2 near jumpholes, lawfuls get level 3's off tradelanes but only level 1 near jumpholes and so forth. Balancing the defenses is far trickier but I don't know much about them so I'll leave it to those who do.
And just as an added extra why not give Carriers the ability to deploy base siege platforms (by module or as standard which ever works) slow firing and slow projectiles useless against anything that isn't stood still but pack one hell of a punch.
