[Phoenix-D]

1a) Passengers as a new cargo type
1b) Cabins to host passengers

1a can be done, 1b not. You just have to assume they cabins are modular and loaded into your cargo bays (reasonable since the smallest component is one KILOTON in size..).

Events can be triggered based on your cargo, so carrying certain passengers could do various things.

2) Minerals (eg.: ore) as a kind of cargo

Possible. However the more destroyable objects you have the slower the game runs (this includes planets).

3) Planetary Defences
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Possible. It does screw up the planet display, though- you have to use the same display as for ships (eg. the population field goes away)

4. can be rigged via invisible off-plane attacking objects (though they'll still appear on radar) I'm not sure how the AI will handle it, and again the more firing objects you have the slower the game runs.

no special patch.