https://en.m.wikipedia.org/wiki/Fitts%27s_law
It may also be interesting to model the state of the keyboard hand. Instead of allowing the computer to access keyboard shortcuts directly it could be forced to operate a virtual hand that is in turn operating a virtual keyboard. Constraints could be added to the speed of various finger movements. This provides balance but also captures authentic strategic tradeoffs. Like the resting position of the hand. I imagine if you had a nice visualization it could even reveal subtle optimizations that were practical for humans.
USB has quite a bit of limitation for HID's and allot of the gaming mice and keyboards use various hacks to overcome them.
Games and OS also have limits I can easily issue more commands using my keyboard than SC2 can handle so not all key presses will actually register.
Not to mention is that the game actually has to run on regular hardware, start spamming your keyboard in a game and you see the CPU spikes, the game loop also puts quite a bit of limits on how many interrupts per second it can catch, and how long does it take for it to actually switch context (e.g. SC2 build menus).
That said after AlphaSC2 destroys another Korean national passtime I would definitely love to see human like input being used by AlphaSC2.
Not because I think humans deserve a fair fight, but because i think the most interesting part will be to see how AlphaSC2 has to modify it's play style to compensate for the limitations of having to use "meatbag" control methods.
If you want "fairness" you can limit the instructions to what keyboard and mouse can actually interpret as in the limited latency between instruction that both the game, the OS, and the hardware can support.