This a great idea, It allows for the highest ranked players something new to develop whilst incorporating further risk when building up moons
However is it really required?
A colony should be placed in as many galaxies as possible...each with a moon on which a sensor phalanx is built that can cover that particular galaxy.
Limiting the number of planets able to be phalanxed by a single player will incorporate teamwork, as working together an alliance should be able to phalanx any planet in any galaxy, negating the need for an inter-galactic phalanx.