We're actually keeping an eye on the idea of recording and playing back games. There is still some uncertainty about whether current ideas would/should work, so it might not happen for a while, but this does seem to be a possibility. There shouldn't really be any noticable lag caused by recording, nor heavy disk space requirements, but the game also isn't built for playback and recording, so any such system might be a bit clunky.
For instance, what if you're watching a recorded game and click on a building and try to issue a new command? Surely this sort of thing should be blocked if you want accurate playback. It'd be kinda annoying if you did something by accident and your whole playback got messed up because of it. On the other hand, it might be interesting to explore a bit of a "what if" scenario. Of course you could experience playback from another person's perspective, and thus be unable to issue commands. But then you also couldn't check on building status, such as research progress, or vehicle/structure kit building progress.
Also, there is the whole issue of interfacing the playback and recording with the game. How do you start it? Save recorded games? Start playback? Even if we have the technical knowledge to record actions in the game, and replay them, I wouldn't exactly know how to incorporate controls for such a system into the game. (I'm not really sure how the menu system works for one thing, so don't just go asking me to add new menu options).
But yes, I still like the idea of some sort of recording and playback.
The attack move command idea is also nice, but doesn't seem to be feasible. Changing unit behavior isn't really such an easy thing to do. At least not in most cases. Minor tweaks, were the old code is still used might be possible, but this is too high level of a change. But yes, it's nice to have this under consideration if some increase in knowlege changes the reality of this.