preferably a variation on the shortcut Go to Next Keyframe/Layer Marker (k). Say, alt/option + k or similar.

I think ideally the Go to Marker Out Point shortcut would take you to which ever is next: either the maker's in point or its out point, so you could quickly navigate through a comp's layer markers using the same shortcut and not have to alternate between pressing k and whatever the marker outpoint shortcut would be.

Same for 'Go to Previous Keyframe/Marker' shortcut. There would be an equivalent shortcut, say alt/option + j
And, again, this would take you backward through all marker out and in points.

Thank you