I'd imagine that many Americans in this ATL would be very pro-metric if this were the case.
Not necessarily. I mean, take a look at the Russian Empire - to this day, it still steadfastly holds onto its own system of measurement, having managed to basically merge it into part of its empire. Its client states in the Balkans, be it the South Slavs or the Greeks, also enjoy widespread use of the Russian system. And, to this day, the Chinese old units of measure still enjoy some use in day to day life, especially outside the capitals.
I mean, technically, all the nations have adjusted to the metric system, but Russia has had its system of measure tied into its national identity. And long as there is a big enough internal market, it still becomes profitable to use the old system, and the conversion costs can be eaten as well.
OOC: The US and the UK both don't use the Imperial system, only the United Kingdom and the Commonwealth/Empire ever did, and it wasn't put into place until the 1800s. (1824, but just guessing. been a while since I checked) The US uses the US Customary system, which is based on the "old" English system prior to that. About 1/4 of all measurements differ because of that, roughly.