Got a few of ideas in that direction,
One is simply to not allow players to visit planets owned by someone else in the team. Creates a good teamwork strategy here since it means you need you work out resources and co-operate on that front too. This would work great with massive maps where there is a bit of flexibility behind empty planets and such.
Ah, but what happens when two allies both attack the same enemy planet simultaneously? It would feel rather arbitrary if travel to a planet was disallowed simply because an ally already has a convoy in-transit.
Another is like mean RTS games that have allies and have a passthing through feature; where the team mate has no control with your factory levels or ships, however just sits perched on the side happy to defend that planet from others until it moves on.
Not impossible, though the code isn't really designed for it.
Either way, keep up the great work!
Certainly will. Thanks for playing!
Please let me know if you come up with any other thoughts on the subject; I always like to hear ideas and feedback.