Something just popped into my head and it might be useful to someone.
You know how if you hit level 9 or whatever you can establish a stronghold, right? We assume you’re under the aegis of some king, because otherwise anybody can just go out and establish a tree fort or whatever in the empty howling wilderness.
Second, and here I’m mostly drawing on a vague understanding of how the Vikings handled it when they conquered England and how the Romans handled it in general (so it might be horribly off-base): if you serve the king as a soldier, eventually he grants you citizenship (if you need it) and a plot of land. A regular old soldier would go to war and come back to a cottage or something. But big heroes / warlords / generals would come back and get control over a big area, maybe even become the new king / emperor / topbigman.
Using 9th level Baron controlling a keep and village plus surrounding countryside and 1st level as a Veteran with a cottage, here’s what I came up with.
1st: Cottage and small plot. You can retire and feed your family plus pay your taxes and sell a little surplus. You get a vote.
3rd: Larger farm with a house, requiring lots of your children or else hired hands to manage fully.
5th: Townhouse or large farm as above, plus some special right – maybe you hold a license to be a miller, or a village mayor. You’re one of the dozen important people in the village.
7th: Townhouse and large farm, plus an exceptional right – a guild head, tax collector, command of a few hundred soldiers, or some office at court. You’re the most important person in the village, or one of the dozen important ones in a town.
9th: Right to build a keep and maintain a village, plus a townhouse, plus some great office like warden of a forest, command of a thousand soldiers.
12th: As 9th but you might get a special office like ambassador, general, or admiral.
15th: As 12th but also supervision over a dozen Lords (9th) as a Duke-equivalent, and you’re counted as not much less important than a Prince – one of the dozen important people in the kingdom.
20th: Just go out and crush some jeweled thrones under your sandaled feet, because you’re only less important than the king because he’s the king. If you found or conquer a neighboring kingdom, maybe your old king would like to style himself an emperor – or maybe you’ll beat him to it.
I haven’t read ACKS but maybe this is how they handle it? I think it makes sense for the first generation after conquest, but the Emperor’s kid is probably gonna be a snotnosed little 1st level punk. At least, unless there is continual warfare, the 20th level king’s kid will end up being 12th or something, and his kid will be 6th, and his 1st (if not degrading faster). This assumes the king refuses to let his kid be a worthless shit and forces him into combat training.