There is one issue I see with the flag rotation:
Currently, the submission of older flags is enabled. But in the future this will not be possible anymore. Seeing how people constantly go on a reset spree on machines like e.g. Traceback, this will cause major issues. Imagine that you just manage to get the flag right before it gets reset. Now, when you submit the flag (which takes at least a few seconds), the flag is invalidated and a false flag submission gets logged on your account. Doesn’t seem fair to me, to be honest.
On machines like Traceback you also just can’t get right back to the user/root account. So you might happen to repeat to submit an old flag again and again, simply because some players reset the machine, right after it booted up, again. Sure, there’s a 2 minute waiting time before it gets reset, but that might happen to be just enough to get the new flag, but not to also submit it.
Just my 2 cents 