This is going to be the thread for discussion on this idea. I previously posted part of this as a comment in another thread. To make sure that no information is lost to those who didn’t see the initial post about this I will have it copy pasted after this paragraph, along with the comments I received from Rathalos and I’ll add my responses to those comments as well.
My initial comment:
Without creating an entirely new thread for what I want to say, this thread seems like the best fit for it. This will mainly be concerning other space civilizations I plan to feature in my loading screen project for the space stage portion of it. Since part of the plan would also be to add these civilizations into the game as rare encounterable civilizations I will include some of the possible game aspects for each of the different civilizations.
- Humanity
Going with my head canon that Thrive occurs in the Andromeda galaxy, Earth wouldn’t be present within the Thrive galaxy. Instead humanity would be a colony that has lost its means of reconnecting with Earth and the rest of humanity. This would mean that the home world of humanity would be a randomly chosen continental planet (in game at least). The ships for humanity would resemble oceanic vessels a lot, with military vessels having some of the largest primary battery guns of any civilization. Humanity would also utilize more physical munitions compared to energy based munitions.
archetype/philosophy: Explorer-human
The human civilization would be very curious. While they would take some time to get a good foothold onto their initial planet they would eventually attempt to rapidly map/survey their galaxy and contact every species they can. When the player begins building the ascension gate, humanity would offer aid in the form of materials as well as protection for the ascension gate from attacks.
- Hyper advanced aliens
I haven’t come up with a name for this civilization yet (as well as many of the other civilization ideas I have). This group would be influenced heavily by the Illuminate, Covenant and other highly advanced species from other media. However, in order to keep the vision of the player being the first to reach the space stage, this civilization would be the result of a future civilization existing in another galaxy finding themselves losing a war against another even more advanced civilization. To avoid complete destruction they would create a time rift to create a new home within their past. They would drastically change the ocean world they found themselves on into a large planetary religious site. With influence from the illuminate, this group would be given a more marine organism motif with their structures and vessels.
archetype/philosophy: Cult - “–”
This civilization would rapidly increase their scientific knowledge compared to other civilizations. This would result in a technological stagnation rather quickly as well. Diplomatically they would be easy to work with as they are looking for allies for their conflict in the future. However, when the player begins building the ascension gate this civilization would become rather aggressive. They will attempt to gain control of the ascension gate from the player. Unlike a civilization with the regular cult archetype, this civilization would move the ascension gate closer to the black hole at the center of the galaxy as they will attempt to build it around the black hole to summon a deity to assist in their future conflict. (Ai civilizations would be unable to continue construction or activate ascension gates to avoid players letting ai’s construct the ascension gate to avoid the material cost of the ascension gate)
- Hivemind
This civilization would be influenced by the Termanids, Tyranids and Arachnids. This insect like alien hivemind would be a non-space faring civilization that later on in the space stage would become something akin to a stellaris crisis event. Their home world would have an atmosphere choked with air born spores. This world would not be habitable to any other life in the galaxy. After the planet and system are surveyed, civilizations will begin to quarantine the system and avoid it as the spores that exist on the planet are revealed to be able to survive in space for a short time, but could also cause entire planets to be quickly taken over from just a few spores. When they become space faring their ships will be bioships and resemble members of their species
archetype/philosophy: hivemind (since it is an organism trait this will be the only civ to have this as an archetype/philosophy)
Closer to the end game portion of the space stage, a popup would appear about a ship from an Ai civilization escaping into the quarantined system. This event will begin the transition of this hivemind civilization from something they has been ignored for now into a major threat. The initial expansion would be slow as they take over the other planets in their home system, but once that has been accomplished they will begin to, starting slowly, expand to other system (regardless of ownership, present colonies, etc). If not dealt with quickly their expansion will grow exponentially. A tech may become available to research that would allow players to use their warships to burn away atmospheres of planets that have been infected by the spores, leaving them as scorched worlds.
These are the only ones I have though about mostly so far, but I do plan to have another based on the cyborgs/automaton legion, terminators/necrons for a robot/ai civilization. I haven’t though about civilizations past that yet and I may think about those ones as I finish the spec evo part of the loading screen project.
Rathalos’s comments:
I think it would be perfectly fine, and probably better, to make an entirely new thread for this.
A personal opinion that I have expressed elsewhere is that I think we should avoid adding specifically humans. Among other things, we don’t know if what we end up with for 3D editor can make humans that don’t look weird.
I would prefer we have something that is clearly a stand-in for humans but also not entirely human. Compare it with Kerbals for example. (I would also like the their species’ “story” to be one of the potential selections for if you start in a later Stage)
I think you might be reading into the Space Stage a little too much as a Stellaris equivalent. I could be wrong, but this seems like an overly specific design that makes sense as a Stellaris-style non-player crisis, but not as something that arises naturally from the normal Thrive game mechanics.
replies to Rathalos
Well it has its own threat now 
My plan already was to have humans play a minor role within the loading screen stories. However an idea I came up with this morning would be to have the interactions be through a ship’s AI, with every human on the ship in cryosleep. This would avoid having an actual in game model for humans, but would likely have a darker backstory for humanity as it would be mentioned that Earth has been ruined.
That is still a possibility and could be a different civilization compared to anything related to humans if decided. However I probably wouldn’t feature them heavily in the loading screen story in order to avoid that civilization from having a story written out already.
The initial idea for that civilization and its function would be more like a stellaris crisis in how it works, hence why I described it that way. To avoid the more crisis like version of it, adding in influence from the Formic civilization from the Ender’s Game series would have the civilization behave more like a regular civilization. Combat wise they would use drones to swarm enemy positions while the queens and high caste members guide and rule their worlds.
For the civilizations I see there being a few ways we handle it. Some civilization featured in the loading screens would be encounterable in game, but not all of them. The only one I want to ensure can be encountered among all of the ones featured would be the sapient Hexaquills. This would mean that the designs and functions of the civilization wouldn’t be held to what we want to game to be like at the space stage, but the ones that are in the game itself wouldn’t be as drastic. The other possibility is for every civ featured in the artworks to have a chance to spawn in the space stage. This would mean I would have to make sure they wouldn’t drastically change a game should one of them spawn (galactic threat civs would be changed to be more normal, but more aggressive than other regular civs)