I think Vedrit's right: TU, Health and Morale are the most important (I completely forgot about morale!).
H-Hour I like your mockup, some suggestions (IMHO):
1) make soldier panel resizeable when therea are less or more soldiers. For example if I enter into battlefield with 4 soldier, could be smaller, with 16 soldiers max size and so on?
2) no names for a soldier? maybe could I set advanced option to see it?
3) soldier with no more TU could have corresponding item with a background that explain this state ? For example with gray background, like in windows, linux, etc ?
4) Can I select more icon at same time ? For example to show health and weapong, or just health?
1. It would expand or contract to the number of soldiers that enter the battlefield.
2. I would probably put soldier names on the long bar below, so that it appears when you mouse over the soldier.
3. I think no-TU is not very useful, since players will reserve TUs for reaction fire, and you could get to 2 TUs but not be able to move one more square, etc. I prefer the light that says only when a soldier has not yet moved in the turn.
4. Well, the icon system would need entirely new features to be developed, so I wouldn't count on it that soon.
None of this is likely to go anywhere for a while, but it's fun to think about different options. There's talk of having a GUI preview feature in the Eclipse IDE some of the devs are working on, and that would make it a lot easier for me, since I'm still learning how it all works and prone to lots of errors. But who knows what the priority is on this, or what priority there is on expanding the cvars available to the GUI. A lot of what I've proposed is not currently possible because the GUI doesn't have that kind of information.
No reason not to think about it, but just putting it out there so we don't get too far ahead of ourselves.