Feel free to grab a mic and a neat recording program and make a speech mod or something. But don't force it on everybody please.
When I think of a Me109 with instruments in feet, mph and psi, and the pilot communicating that way, it gives me "teh gigglez", actually
Additionally, even in the old, non-standardized world, there were only a very few sets of units of measurement in use. It shouldn't be too hard to get used to two, at most three units of measurement. Hell, even today, you'd have to learn conversion from mph into knots...
P.S.: I was one of those who changed the old 1946 speed bar to km/h, mph or knots, as appropriate. Another immersion factor (asides from the speedbar itself
) you'll have to rip from my cold, dead hands tbqh.