Backstory

A minor admiral of the ancient nomadic civilization of the Nacre Concourse has decided to take his young multi specie fleet into a galaxy that once housed a great space empire, and seems to be on the verge of another. He seeks to form a federation bent on peaceful exploits of the fledgling species so that the great fleet need not fear this region of space and may share in the bounty of the region centuries from now. The great fleet feels that it would be better to avoid such a flashpoint, the risks too great, the rewards too little. The hub of the small fleet is a great ship that houses billions, mines asteroids, grows crops, and builds and maintains their fleet. The Nacre have no planets to call their own, and thus have no conflict of territory with the other species, but also lack the ability to have great populations. They fear land, as they are born and die on their ships far into space, though when they die their minds are absorbed into their ship and become one with their ancestors, giving advice to future generations.

Traits:

no colonization - their colonies are super-sized ships that can move and migrate freely even while building buildings (but not ships), but they are more expensive to build than any ship by far and while strong relative to most ships are not cost efficient to use as warships. no colonial base, any improvement that gives a bonus to any planet gives it to the great ship instead, and any boost to asteroids or gas giants only applies while the great ship is deployed to the appropriate type.

no land - they may deploy their great ships onto gas giants or asteroids, reaping the full benefits of having a colony there. their great ships always produce food based on the star of the system they are in, and their planet approval and max population is always that of a tiny class 1 planet. undeployed great ships have a base value of 1 in industry, dust, and science.

ship destruction malus - any loss of their ships renders a large approval penalty to the empire, relative to the size of each ship lost.

nomads - they may have their great ships in any allied system, and deploy them on uncolonized asteroids or gas giants, though having their great ships in an ally's system produces a small diplomatic penalty, and claiming asteroids or gas giants when they are able to colonize them produces a bigger penalty. Nacre never claim systems, great ships are used in calculations instead.

another man's trash - each faction you know of yields +1 industry for your great ships, +1 for each of their systems if you are an ally. Double income from trade, allies also receive this bonus to their routes with the Nacre.

interspecie faction - starts with the ability to offer peace and ceasefire with factions, researching this technology instead results in a population boost for a great ship while it is in a system controlled by an ally.

In the early game they will have the advantage militarily due to their great ship, as it can be used a formidable warship early on, but doing so will put you back quite a bit with little to show for it as you can't take planets. This lack of gain during war discourages without outright denying it, and the lack of being able to harvest luxury or strategic resources promotes trade (and thus alliances). Diplomacy is the strong choice for the faction due to the lack of the ability to create a war machine (should be fairly weak at industry), though you are not defenseless as you can run away from conflict. the ship malus means that during peace your citizens are quite happy, during a serious war they are quite unhappy, though if you are massively more powerful than another faction you can perform 'gunboat' diplomacy without penalty. While starved in industry, they have no need for many planetary improvements, helping to balance this to simply being weak in needed industry, though spamming fleets (let alone great ships) will still be beyond their reach.

Settling in another faction's system will not be possible with the system ownership we have, I believe.

worth a shot, there isn't too many strategy game engines that appear to be able to handle a nomadic faction. yours seemed like it might be able to do it, which is pretty good.