I had this idea as well. It really would make a lot of sense, since all the current troops are tied to the specific kingdoms (or bandits). This would help your own kingdom become much more unique and personal, and could reflect your own combat philosophies. Having a simple tier-restricted troop creator would be great. It could probably be done in a number of ways, but here is one off the top of my head:
A point/level-based system, where a given tier can have troops of a specific level or range of levels, and you spend points based on that to level up certain skills and abilities for them, and they'd get a certain amount of money (or further use of points) for use on gear, all of which is restricted to certain quality levels for the tier. Furthermore, you might get a troop type selection that further restricts/focuses their skill/equipment options, to help ensure you are making troops that fill the roles you want them to fill.
I think it would be better if the recruitment/upkeep costs in general were not standardized, since that seems pretty gamey to me, and if they weren't I'd say that the cost of the troops would depend on how strongly you built them. In general, even with the normal troops, this would allow you to choose troops based not only on their quality and how well they fill their role, but also based on how expensive they are. But that's probably something for a different discussion.
A point/level-based system, where a given tier can have troops of a specific level or range of levels, and you spend points based on that to level up certain skills and abilities for them, and they'd get a certain amount of money (or further use of points) for use on gear, all of which is restricted to certain quality levels for the tier. Furthermore, you might get a troop type selection that further restricts/focuses their skill/equipment options, to help ensure you are making troops that fill the roles you want them to fill.
I think it would be better if the recruitment/upkeep costs in general were not standardized, since that seems pretty gamey to me, and if they weren't I'd say that the cost of the troops would depend on how strongly you built them. In general, even with the normal troops, this would allow you to choose troops based not only on their quality and how well they fill their role, but also based on how expensive they are. But that's probably something for a different discussion.