Something I've been thinking about a bit recently. So of course the Imperium is a very unequal place with the upper classes living in unimaginable luxury and the lower classes living a rather subsistence existence, it wouldn't be the grimdark place it is without a healthy dose of inequality! That doesn't mean that we can't take a look at the things in the Imperium that help to maintain and enhance this inequality though.
In particular something that I think goes a considerable way towards helping to maintain the inequality of the Imperium and also its somewhat feudal and reactionary nature is the existence, and efficacy, of anti-aging drugs (juvenat treatment). The 40k literature is replete with examples of high ranking Imperial officials and aristocrats who are still very active and engaged in worldly affairs at ages of several centuries. It does not, however, give the impression that these wonder treatments are available to the masses, most likely because they are prohibitively expensive. I also see the potential for something of a snowball effect to occur since people, particularly wealthy merchants, tend to accrue wealth over the course of their lives. As a result having an extended lifespan would provide a longer time to accrue more wealth, and leave them in an even better position to afford the next round of juvenat treatment. Imagine how rich Warren Buffett would be if he could live to 400!
I see this giving rise to a real imbalance with the rich and powerful having lifespans of ~400-500 years while the rest of the population would have lifespans more like those of the Western world today. At least for the middle classes, probably even lower for those at the bottom. So the upper classes would live at least 5 times as long as everyone else, if not longer. This does a number of things, first as I mentioned above there is the 'snowball effect' that the longer the upper classes live the richer and more powerful they get widening the gap in absolute wealth between those at the top and everyone else. It also raises the possibility of having multiple generations of the same family serving the same wealthy aristocrat consecutively. I've mentioned this elsewhere before and it enhances the feudalistic tendency of having one mid-class family performing the same duty for the local family of aristocrats for generations, as now they are not just serving the same family but the same person. I can imagine that on the rare occasion when one of the later generations of the servant family gets spoken to by the aristocrat they might well be told 'I remember you great-grandfather, he was a very solid man and a good servant'.
If the rulers of the Imperium are very long-lived with lifespans of centuries it also allays a problem that I know Kage complained about on more than one occasion in the past, namely the cultural inertia of the Imperium. The crux of the issue is how can the same cultural phobias and prejudices be maintained millenia after the original cause has vanished considering that dozens of generations will have passed? The answer is perhaps that while it may be true that a millenium is dozens of generations have passed for the toiling masses, for the ruling classes a millenium ago might be the days of their grandfathers or great-grandfathers. In terms of time span the result would be that the ruling classes would have the same view of the Norman conquest of Great Britain as the population at large does of the second World War. Since it is the ruling classes that by and large shape politics this would help to support the cultural inertia of the Imperium.
Anyway that's enough for this time I think,