The modifiers live on the home row now. A letter held is a Shift. A letter tapped is a letter.
But the hand that wants to write fast rolls across itself. One finger into the next. The held key and the tapped key belong to the same side, and the meaning blurs. Chaos.
So: bilateral. The modifier fires only when one hand holds and the other answers. Left holds, right taps. Right holds, left taps. Same hand, nothing.
It is the shape you have always used — Shift pressed on the left while the right hand types the letter. Only now every key on the home row can be that Shift, if the other hand is listening.
Two hands. One mind. A conversation in every shortcut.