Back in the days of say, Napoleon, or Empire, we used to march around with armies of rank and file troops, with the odd Guard or unique unit thrown in for good measure. And that worked a treat, in my mind. You really felt the elites were the elites, a cut above the rest.
These days, we can build entire armies consisting of nothing else but the cream of the crop. Now, in and of itself, there's nothing wrong with that. I'm sure pretty much everyone here has already built a Praetorian army or the like, it can be enormous fun to watch that army march forth and trample the enemy into the blood-soaked dust.
But by having that possibility, we arguably lose a certain amount of flavour and diversity. That's why I would be for a limited unit system, not unlike that we're getting with the Tomb Kings. One that makes elite units available in small quantities per appropriate building.
A system like this would also work beautifully with this time period. One where levies made up the bulk of one's forces, supplemented by smaller numbers (e.g. two or three units) of more professional soldiers to provide a solid backbone to armies.
Let's say, for example, that a level 3 barracks grants you access to Thegns, but limiting them to a maximum of 6 units. Building that same building in another settlement brings the total number of Thegns you can field to 10. Ceorl Axemen, on the other hand, would not be limited under this system, as it is but a unit of armed peasants.
Thoughts and opinions?