Palpatine has shown us that FFG isn't afraid to make an upgrade card that will fill multiple slots on a ship. Now putting aside the arguments about what that means what else do you think would make a worthy two, or possibly even more, slot upgrade?
I have liked the idea of a non-discarding missile or torpedo that could fill two slots. Having other weapons that fill multiple slots seems very possible.
When it comes to what the multiple upgrades mean I suspect that the symbol will reflect type and that an upgrade could have multiple types and get treated as all of those types simultaneously. Two crew icons is still just a crew. Have a crew and system icon the upgrade is now both types at the same time.