Are there any plans to add more shipwrecks for investigation missions?
TL;DRYes, they will use more shipwrecks as soon as they get them, but making walkable wrecks takes much more work than ships breaking up in-game.
Yes - as soon as they're given them, they'll use them. Currently when the ships break up, they're not like the shipwrecks that Players can walk around right now; they have to put a lot more effort into making those shipwrecks as opposed to those you might actually witness being blown up. There are a lot of collision issues, and other things that Players wouldn't see because after breaking the ships apart, they then have to do a lot of work so that the Players can actually navigate the wrecks, and that they "hold up" when you get that close (I interpret this as meaning that they still look good, but it's possible that it could be meant literally). On top of this, the ships are getting bigger and bigger, and he (Luke) will only ever ask for the biggest ship lately because there's not really much to do with something as small as the Hornet. Incidentally, they're creating (or have created) an FPS combat mission within a wrecked Starfarer, and have prototyped an entire mission which takes place within an 890 Jump.