I really want to see recorded games now that we have defcon schools and tournaments going. Plus, considering the game already seems to download an entire match when you join late, it might not bee too hard to just write it to the hard drive and give players control over the speed. It could provide match conformation and valuable tutorials on advanced techniques. Plus, you could see after the game exactly how your opponent beat you and how he snuck past your anti-sub carriers.
Could the data that we already download just be saved to a permanent file? It's already stored on the server since it can be sent to joining spectators. Would it be difficult to save it to a hard drive if a player chooses. When it is played back, it would act just like a spectated game when you right click, but trigger it so that the viewer gets control over the time. The only potential difficulty would be if they wanted to add rewinding.
I would really like to see some interface improvements though just to make the game feel nicer. Hot keys for things like Radar, Population, Comms, etc and fleet building just so I can build those smaller fleets without wasting everybodies time in real time. Unit ones wouldn't be bad either, anything to increase efficiency and help me bug players less with my real timing.
On the interface front, I would also like to see team colors changeable from the style menu. I can't stand the blue as it is so dark and difficult to see. I've tried everything to make it stand out more including changing to a different style that didn't have any blue, but it is still difficult to see. The ability to choose a color such as magenta would be nice. It would also be useful for picking a new color to distinguish orange and yellow.