Why transition to a double key combo rather than use CapsLock as Esc? The other quite useful "universal" key is the § key on a European mac keyboard (which is for some insane reason just under Esc where ` normally would be)

Because your fingers stay in the normal location. To hit escape, I have to either lift my left hand or rotate sharply at the wrist.

Yes, but you capslock is more accessible than the ctrl key in my opinion. I quite like the option to remap capslock to both ctrl (when used with another key) and to esc when pressed alone, that was suggested in other comments.