Similar to how FozzieSov (which I am not a huge fan of) tries to spread fights out at nodes, a similar thing could be done with structure fights. Nodes spawn in adjacent systems. Players can fight over them. If a node is destroyed, the damage cap of the citadel increases by a fixed amount/percent. If the node is successfully hacked, the reinforcement timer decreases by a certain amount/percent.
I’m not too picky on the exact benefits to the attackers or defenders. You can give ways to both sides to modify the timer or the structure resists or the damage cap, etc. Just that this may be a way of spreading out fights, making undefended citadels die even faster, and giving both attackers and defenders good options to manipulate fights.