I have this idea, but not sure if it's possible to implement:

Allow harvesting ships to have multiple source planets. For instance I have 4 Outposts at my home base, I would like to be able to set all 4 planets as source and set my colony as destination. This will cause the harvesting ship to:
A. Stop at each planet to pick up available resources.
B. A and if cargo hold is full, return to destination planet.

Possibly a skill may be required, which would allow to make 1 additional stop per point.