I like this, especially now that colonies you control yourself and friendly fleets of your own faction is a thing.
with a cost of DP needed to be filled with combat ships depending on how far they're going and if the starting point / colony destination is in a contested system/has pirate activity
I think the combat ship escort should be up to the player rather than requiring a mandatory amount of escorts. It should at least suggest an escort size to the player though based on hostile faction activity in/around the destination system/colony.
aand, a sister mechanic where when you send your freighters off to make a jump you can request your colony sends it back out with an escort from the colony to stop off at a pre-determined point and then wait for you with an Intel Entry that lets you know when they should have arrived by, with the option of for it to just wait for you until it's only got enough supplies left to make it back home and return if you never show (safest option) or to wait until they're forced to jettison and stabilize their cargo and then mothball themselves to wait for you to come get them when you can (chance for their cargo / mothballed ships to be in tow of a nearby scavenger when you show), or to call for you with a distress beacon (which gives a solid chance you'll have to defend them from pirates when you get there) or for you to call them to you with your own distress beacon (same)
This is interesting as well, though I think instead of waiting in space they should land at or orbit a colony/planet to wait for you - that eliminates a lot of extra potentially flawed decision-making by the AI controlling the transport fleet and frustration on the player's part. And obviously as you said, having them come back to you at all rather than just waiting in storage at the colony after delivering the goods would be optional since you may just want to send your exploration goodies home while you chase down a bounty or two on the way back.
Also as additional options, in addition to dropping off whatever cargo at your colony/storage you should be able to tell them what (if any) resources to load up on to bring back to you on their way back (for instance, bringing back all the supplies and fuel they can hold on their return trip). And instead of the colony providing an escort on the way back (it would be a long way to go), have options to either return at best speed (just keep any surviving escorts you sent with them originally) or reinforce and return (the colony draws and autofits ships from storage and queues fresh construction to replace escort losses before returning, possibly delaying them).
