I was able to achieve this. It's finicky and requires multiple save/reload/game restarts as well as a little light save file editing. I'll detail later when I get home.

I second this. For reference, the game does not consider a ship in space a "map" therefore does not allow you to unload the map on the ground.
I did not check how the mod is coded, but I imagine this could be achieved by removing the check to "not unload last colony" entirely, if no better solution is possible.

That being said, if it properly allows to unload starships that'd be great too.

It has allowed me to use multiple map types. I've been able to take a ship (many different ones as of now), and migrate it, almost unscathed between ground, SOS, and also Rimnauts maps (all handled differently by the game).

100% of this functionality has come from save file editing, extremely light duty I might add. However, pawn handling breaks doing it this way.. in 100% of cases, they (vehicles, animals, mechs, anything that counts as a "pawn") appear in drop pods and land in a tight cluster somewhere near the center of the map with their inventories intact.. i merely use Character Editor to teleport them back where they belong. It's a mild inconvenience considering what it allows me to accomplish and still maintain a 360tps.

Vanilla map type:

<li Class="Settlement">
<def>Settlement</def>

And SOS2:

<li Class="SaveOurShip2.WorldObjectOrbitingShip">
<def>ShipOrbiting</def>

Also Rimnauts if that interests you (it should!):

<li Class="Universum.World.ObjectHolder">
<def>Universum_ObjectHolder</def>

These are the only lines in the save file that actually matter for this. You're basically just switching your map type to something Faction Manager accepts.. which is only the vanilla type right now. A whole settlement in a save file would look something like this:

<li Class="SaveOurShip2.WorldObjectOrbitingShip">
<def>ShipOrbiting</def>
<ID>419</ID>
<tile>77310</tile>
<faction>Faction_62</faction>
<creationGameTicks>1248560278</creationGameTicks>
<questTags>
<li>Quest13.map</li>
</questTags>
<drawPos>(0.0, 0.0, -150.0)</drawPos>
</li>