I envisage these leading to trouble.
For example, my KVM box intercepts a sufficiently rapid double press on
(either) Control key, and then expects a CR to switch computers, or ESC
to cancel (and maybe there are other keys I don't know about).
I quite frequently start typing a command by pressing the Control key,
then change my mind and let it go again. I might sometimes hold that
key while trying to decide what I want to do. The same surely applies
to Meta as well.
To make this work on a tty would involve fancy work on the keyboard
layout if it's even possible. On a Linux console, it might even need
enhancements to the kernel.
I'm not sure binding our shift keys to commands, or even prefixes, is a
good idea.