A next unit button would be excellent.
I will add another feature: A checklist of 'things to do'. The player can check or uncheck whether he cares about some of these, but there would be one all-encompassing checklist, with things like:
* Visited corps list (movement, reinforcement)
* Visited fleet list (movement, reinforcement)
* Visited all free states (reinforcement, economic)
* For viewing, a master list of all owned minors, with "free state" and "conquered" listed.
Note that some of the above could be done very easily by simply putting sort buttons into already-existing interface windows. For example, if we could sort the corps list by their current status (foraged, normal supply, not on map, etc.), this would allow checking the "list" without having to scroll too much.
Another interface window that could use sort buttons is the minor/major status window. This is the one that shows a cross-grid with the major names across the top and all the nations (major, then minor) down the left. If there were a drop-down box at the top with
* free state
such that, when chosen, the owner's column is sorted with the selected value at the top, that would REALLY help. Then, one could look over one's list of free states at a glance. The other information would still be there, but would have to be sorted "normally" to see without scrolling. Note that this would have the side-benefit of allowing the window to be smaller.