The ideas I have can roughly be boiled down to space vampires or space Golden Horde I guess.

Basically for the first the idea is that the nation's aristocracy have through some kind of expensive process which has rendered them functionally immortal and comes with a host of other boons but at the fault of needing constant reapplication of the process which had some kind of nasty side effects (I don't want them to literally be vampires so I'm gonna mix stuff up but it's the idea that came immediately to mind). So the immortal and detached rulers see the commoners as an expendable force for work and warfare and keep them in line by dangling the carrot of immortality for those who distinguish themselves. I want to like this idea but it's still super loose and I haven't gotten it to feel right yet.

Second is exactly what it says on the tin. Haven't put much thought there.  

Nothing is final and I don't even know if I want to go forward with either of these, just kinda playing with ideas right now.