I think there should be space battle missions in the campaign as well as in the crucible. Right now the ships that we have are just there and don't do anything except look pretty, at least the sparrow serves an actual purpose. It would be nice to actually be able to do something with them and it would be nice to be able to get something from the ones you don't want. The introduction of space battles would allow for the ability to actually do something with your spaceship like upgrade the armor, weapons and engines, as well as fight other spaceships with it. You could also add in cosmetic upgrades that are similar to the current shaders that you have for our characters.
When I finally got to Mars, I was hoping for a mission that would have me fight my way down to the surface. It would have made for a good mission to have to fight your way through a Cabal orbital blockade in order to get to Mars. It's obviously too late to add that mission into the game, but nevertheless it would be nice to have campaign missions that take place in space. It would also be nice to have maps in space that you can explore... basically have a patrol mission similar to the patrol missions currently available, only they take place in space. It feels like there isn't really anything tying the spaceships into the game, almost like they were an afterthought when the game was being made.
Incorporating this would allow for more options with Shipwright, but it would also allow for an opportunity to have another vendor (e.g. a salvage vendor). It would also allow for you to open up parts of the city below the tower. For example, to get to the salvage vendor you have to go down to the city and walk to a shipyard. It would be in the shipyard that you could find the salvage vendor. You could have different options with that vendor where you could sell the spaceships you don't want to him for different options like: ship parts (for doing different upgrades to your ship, similar to weapon parts), upgrade parts (e.g. a new engine, armor or weapons) or currency; and you would be able to pick which option you want. You would get a determined amount of currency, access to trade for different upgrade parts or a set amount of ship parts, all depending on the ship and it's rarity that you are trading into the salvage vendor. If you choose to trade for upgrade parts a list of available parts would show up in pairs of two, you would be able to pick which combination of parts you want in trade for the ship.
The salvage vendor would only sell upgrades and what not, he wouldn't sell ships. You could then have a second vendor at the shipyard that sells ships and sparrows. It would also be nice to have weapons for your sparrow, since there are alien versions that do have weapons on them. It was really confusing to me that my sparrow didn't have any sort of weapon system on it, especially when I encountered the enemy version for the first time on the Moon. I was sitting there thinking, "Why can't I fire back?!?!" That is definitely something that would be really nice to be able to do.
You could incorporate this as an Expansion just like "The Dark Below". Only I would love to see new maps added in, instead of just new missions on the currently available maps. Doing it this way would also allow for you to open up the city below the tower. In order to get to the City below the Tower, there is a space ship in one of the docks in front of the main courtyard with someone standing in front of it. When you walk up to them the option pops up to interact with them, but instead of saying "Interact" it says "To The City", or something like that, above the button you need to press. It would then drop you off in a specific spot down in the city. You could still go to orbit from the city like normal, but if you just want to go back to the tower without going to orbit, you go back to that ship where it dropped you off. It would be the same ship with the same person standing in front of it so you could find it easily, but it would obviously say "To The Tower" when you interacted with him/her. You could possibly add an option while in orbit to skip the tower and just go to the city, but I think it would be better to have to go to the tower first and then the city. Either way, it would be good to have an option to go to and from the city and the tower without having to go to orbit.
Everyone that I know would definitely preorder an expansion that introduced all of this. To wrap this up is a bullet list of the things I talked about.
-Access to the city below the tower
-Ability to go between the Tower and the City without needing to go to orbit.
-In the city is a Shipyard, along with other locations for more variety of vendors.
-In the shipyard is a salvage vendor that you can sell your unwanted ships and sparrows for an option of parts, upgrades or currency.
-Salvage Vendor doesn't sell ships, just parts and upgrades.
-In the shipyard is a vendor similar to Shipwright who sells ships and sparrows only.
-Introduction of space battles into the campaign missions as well as the crucible.
-Being able to upgrade your ship with different engines, armor, weapons and cosmetic upgrades.
-Weapons for the Sparrow.