I think Chris needs to avoid having a freeform plot like the Yggdrasil and actually make things happen. The elemtns outlined above are really just to lend him plausibility: Chris needs to gather a firm, interested player base and lead them into doing something instead of just waiting for something good to happen.
I heartily recommend having a cause or a direction beyond 'plundering the next cargo freighter' to avoid slating the pirate plotship for only one thing. That doesn't mean you should be a Captain Harlock or anything like that; what I mean is that if you have a long term, concrete goal to go after, it will give direction, cohesiveness and longevity to your plot. It all depends on how strong your premise is.
I'll give an example. We haven't learned much about the Lorath, so, I'll pick something up from them.
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Following the devastation of their homeworld and Queen Harrike's support of Yamatai - to the displeasure of many of her subjects - some Lorath soldier decided to take things into his own hands and reap revenge on the people whom robbed them of their skies. Gathering supporters, he took control of one of the few Zahl cruisers the Lorath had hastily built and took off with it to go and do his own things.
That Lorath commander would pretty much intend to strike back at Yamatai and somehow hurt them for revenge (Yamatai is well established, while the Mishhu are unknowns: thus, the YSE is easier to strike at). He'd probably be seen as a sort of hero by some of his people, even despite his actions going against the treaty because there's a lot of underlying resentment in the air right now.
There are a great many things that said Lorath privateer could aim for beyond the scope of just raiding cargo ships - which would probably just be a means to keep fighting more than anything else.
- Find and secure a secret hideout for his small following.
- Gain supporters, possibly making contact with either Nepleslia, Elysia or the rogue QIS. (new crewmembers, perhaps not lorath as the Lorath privateer gains understanding of the amount of discontent in some parts of Yamatai).
- Gather more resources and materials to expand operations.
- Covertly support the interests of the Lorath.
- Secure and try to implement whatever technology would turn up in their plunder. Resources back with the main lorath people could be greatly helped by that too, though advances would be hard to justify - the pirate ship would have to look unrelated to the lorath people not to draw too much ire from the Yamataians.
- When favorably supplied and with decent assets, try to engage and destroy SAoY and SMX vessels in well orchestrated operations with odds in the pirates favor - preferably to secure worthwhile objectives... thanksfully, odds are that some regions are softened up by their respective opponent of the side the pirate ship (& possible assembled taskforce)
- Possible late advancement for that plot could be to actually become able to seize control of a star system owned by either the Mishhu or Yamatai and be able to secure it for their own use. This would be showing up as a very visible threat, but would also count as a big victory for the said pirate plot.
- try to deal with the reversals and harsh situations which will come up here and then: the goals are ambitious and daring and could lead to much risk at one point or another.
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You certainly don't have to follow this, but I think it's the sort of epic feeling you should go after.