I was thinking that it would be really neat to be able to rebuild units explicitly rather than have them rest in a high morale province and take many game days to recover. You should be able to place a unit in a city with appropriate buildings and be able to say rebuild this unit please much in the same way as you can repair a damaged building. That way you can expend a proportion of the resources needed to build a new unit but rebuild an old one. The amount of resources should be less as the core administrative portions of a combat unit are mostly unaffected by combat losses and these are often expensive in terms of trained manpower and equipment.

Most types of units should also be allowed to convert to a similar "type" of unit in the tech tree. For example, you may have too many Armored Cars and want to convert them to say, Light tanks. There should be a conversion schedule that allows you to do this taking into account that often the core HQ and admin elements of a unit are quite similar and just need a bit of retraining time and the combat elements need to be re-equipped and trained - this process should be cheaper and shorter than building a completely new unit. I would suggest that all Infantry-style units could be converted only to another Infantry-style unit, Armor to Armor, Air to Air, Naval to Naval and probable Specials cannot be changed at all.

Finally, players should be able to disband units and recover at least their manpower and perhaps a bit of Steel and maybe Goods. Later in big games when food becomes limiting this would be a great way to help stave off starvation