Actually , as far as I have understood it's "only" planetary landings that will be implemented within a year after release as a first expansion. Ship/station interiors with the ability to walk around will come in a later expansion and maybe these things will be split up into several modules
As I see it FD will over time be filling in more and more details into the game over the years to come. The first release will give us a galactic "overview" of the game. The first expansion will open up the planets for exploration (maybe just from the ship or possibly with some sort of landbased vehicles), but since you won't be able to walk around as a character you can keep the details on these worlds relatively "low" since you won't be interacting with them that close at this stage. When eventually you will be able to walk around inside your ship and also leave it they will have increased the level of detail further on the stations/planets/cities.
As has been said many times before. The issue with using procedural generation is not generating enviroments. Filling out the entire galaxy with planets that has the same graphical quality as GTAV is "easy". Just to clarify what I mean with this. Let's say you want to create cities throughout the galaxy on every single earthlike world. You could just create one really good looking building and then tell the system to repeat that in a gridlike pattern at certain points on all of these worlds. Done! But as you understand eventhough that building might be beautiful on its own it will still look like crap due too the fact that it is the same building repeating over and over again making all the cities look the same on every single world.
The challenge with procedural generation is not the scale of the gameworld that you want to make. The challange is to make it seem varied enough, so that the player doesn't pick up the "repeating patterns" as easily. So how do you do that then?
Well, if you take the same building but tell the system to randomize it's size, rotation, color and placement (so everything isn't placed in a perfect grid) the cities will already look more alive and real. If you then make a lot of other buildings and put them into the system then eventually the player will stop thinking about the fact that similar buildings are being reused. You could even make a system that create the buildings themself out of smaller buildingblocks so even more variation can be achived. The same technique can of course be applied to everything else in the gameworlds environment.
So the challenge with this game when it comes to realizing the world is to have a system that can simulate the layout of planets, clouds, vegetation, wildlife, cities and interiors of stations among other things. Thankfully this type of tech doesn't really need any graphical assets during it's development. You can quite easily test it out with simple placeholder art. This makes it possible to work on these type of things for a long time between other projects. Something I am quite confident they have been doing over at FD for a very long time. When you then finally decide to go into production you can then create the kind of game assets that the hardware at that point is capable to handle and just plug those into the system. Tada! A fully realized world!
Whoa...that went on a bit longer than I had planned!
However, my point with this is that creating all of the planets in the entire galaxy might be roughly the same amount of work as getting a good character system in place in the game. Hopefully they can borrow a lot of code from The Outsider though since that seems to have a lot of the mechanics in place that I envision will make it's way into ED eventually.
