Caps Lock <—> Esc should honestly be standardized on keyboards. Esc is used pretty often in my experience while Caps Lock, being modal, only gets the occasional press even when used.
Was always my first tweak to a new machine - such an obvious change. Moving to a split keyboard gave me three keys at each thumb - the same kind of realization. We have two thumbs that most keyboards map to a single space bar. The thumb is a really solid finger for modifiers.
Another nice thing about a custom keyboard is not needing to map the keys - it's in the firmware.