There's a a lot they could do with player structures.
Right now, they could add mining/extractors on beta islands or sections of the beta islands you control. That would open up the opportunity to charge a fee to let other corps use that land. They could be throw-away structures like incubators and/or have the ability to fuel a shield that reenforces before being destroyed. The controlling corp could also add fixed defenses, something else that would need to be fueled.
For more complex player structures, I'd put them on new continents atarting with an alpha continent. I think there should be an increasingly-costly wardec mechanic (syndicate wouldn't like too much of it) allowing you to attack them so the structures would be fairly safe for the individual, but for the bigger corps they would face the possibility of getting wiped out by rivals periodically(I envision such wardecs to apply everywhere but the A-1's). Hopefully, there would be a new research mechanic with structures, single line factories, defenses, mining, etc...
Sky's the limit for a beta continent. It would be great to make it really hard for an established corp to defend both their beta island structures and those on the valuable of the continents. You accomplish that by having tp's aplenty on the alpha continent, but very few on the beta continent. You'll wind up with some people becoming outlaws on them and starting an interesting dynamic. The structures themselves could be better on them with some unique advantages, worth fighting over.
^ Just some random thoughts.
