The other night when I was playing a Warband -> floris expanded marathon (and also tabbing out every now and then to read the forums) I got an idea of what I thought would be awesome. Combine both leveling systems.
For example using Swadians:
You go to a village and you recruit a Swadian Recruit. As this recruit gains levels he becomes Swadian Recruit (experienced/veteran/etc). This is for free when he levels. This will only increase his stats, this will not change his gear/weapons/etc.
Now you can go to towns or garrisons or something and pay to increase their gear. So for X denars that Swadian Recruit becomes Swadian Militia. This Swadian Militia has better gear/weapons/etc.
It would probably need to do some testing to decide prices, balancing, leveling. Would a Swadian recruit (experienced) become a Swadian Militia (experienced)? Or maybe there could be some design factors here too. Like the stats carry over, so a Swadian Recruit (rookie) and a Swadian Recruit (veteran) will each become different stated Swadian Militia.
This will make godly armies for someone who takes the time to level each unit up before upgrading them into a stronger unit. Or if you pay money right away you can get that strong geared weak stated army quick. etc etc