The artwork is awesome, although there's quite a few different styles. That's not a big problem for concept art, but as you move toward a more complete world I suggest narrowing down the visual style so that its more consistent. This image really stood out to me because it's super cool, but also because it doesn't match with anything else in the document. If there were a couple of these in the same style, marking different historic periods for example, it would feel less random. You also switch between thick lines vs thin lines, different types of shading, etc. Again not a huge deal, but going forward you might want to think about which method fits best. Personally I like the sort of dusty 3D renders the most, they give off a nice steampunk-esque vibe.

As for the writing portion, it's a bit disorganized. I would consider putting a summary at the very top that explains the world from a macro point of view. Highlight the key points, and perhaps even more important what makes this world different from every other fantasy world. When I get thrown straight into early tribes, I think "here we go again, yet another fantasy world that starts with primitive tribes conquering each other." That might be fine if I'm reading a novel, but here I would have rather heard about the big concepts right off the bat. Start right away with "this is a planet with no technology where a huge derelict alien vessel crashed, disrupting society everywhere." A good design document should give readers an idea of the whole within the first page or two. Then get into the details.

The sections are a little all over the place. Here are your section headers:

• Antiquity
• The Exolith Era
• Somnific Ash and New Dogma   (problem: previous sections were time-based)
• Veils     
• The First Nomads    (now we're jumping from an item, to a people/time period)
• Artifacts    (back to an item)
• Guilds
• City    (this is about a specific city, the title should include its name)
• Desert   (I guess this is the opposite of the city?)
• Desert Frontiers    (this section is actually about groups of people)

If you read them like this, the direction is unclear. First we're moving through time periods, but then it switches focus to items, groups, and locations. I would try organizing the sections differently, and be more direct with each topic. For example the section "Guilds" starts with this sentence: "Centuries later, a majestic city grew up around Exolith." What? Get right to the point... this section is about the Guild Council, I shouldn't have to read an entire paragraph to find that out.

For organization, you could have time periods as your "big" header and then smaller sections in between:

• Antiquity
  • What tribes exist?
  • Where were they concentrated and where did they move?
  • Beliefs, technology, customs?
  • What is the cimate, wildlife, etc
• Exolith Era
  • What happened to each tribe?
  • Culture shock everywhere - how did each culture respond?
  • How was nature affected?
• City Era
• What new technologies are found? How did each culture respond?
• Who is in power? Who speaks out against the new way of life?
• Is nature recovering? Forever changed?

There's some really cool concepts in here and nice artwork. I'd like to see more "showing" of the history rather than "telling." For example you wrote "The city has seen booms and busts, witnessed the apogee of bloodshed and the triumph of peace." Okay, tell me about it. You are basically saying "this is a story with conflict in it." Great! Now flesh it out... create some historical events about specific groups of people that you have already established. Work towards populating the timeline for each group of people, and make those events have an effect on their future. It's a lot to think about for sure! But if you build it one piece at a time, you'll end up with a historybook!

Do I think this could be made into a game? Totally. But it will take a lot more work to grab the attention of a developer, as translating all this into a videogame or tabletop game is a huge undertaking. Maybe look for people who are interested in helping with the world building and narrative stuff as well, so that you aren't writing literally everything. Good luck!

Fundamentally, what's the story?  There may be one, big, true story that no one knows, but each tribe is going to have it's own stories and legends.  Some will be true, some will be subjectively true, some will be dangerously wrong.  Many will blend truth, myth and falsehood, depending on where they came from, who was telling them, why they were telling them and how garbled they got in the retelling.  The world arises from the interaction of and conflicts between those stories. 

Your game, as it plays out in the world, is another story, one that interacts with several of the older stories and, hopefully, influences many of the current stories.