My ASI has statute and nautical miles engraved on it, or at least the speeds associated with those units, my POH uses mph for performance, but the world was assembled by sailors so the FAA is correct in trying to ensure pilots can cope with both.
Why do the Swiss insist in using metres on their half million topo for heights, we are not mountaineering when we fly, and unfortunately multiplying metres by three is not safe enough.
Its horrifying to sit in the cockpit of some European aircraft and look at meaningless dials.
Mixed units I am afraid are with us for some time to come, and will remain a trap for the unwary or the hasty.