There is good video about "Imperial VS. Metric" posted by 'Real Engineering' two month ago.
> USA can't go metric
SpaceX already use metric:
> Despite NASA's non-compulsory policy, commercial space manufacturer SpaceX currently designs its systems (e.g. Dragon and Falcon 9) using metric units.
According F9 v1.0 Users Guide it seems like SpaceX mixed SI (preferred) and US units on same vehicle.
FTR, On May 1st, 2016 Elon Musk said next:
> Historical precedent. Mars vehicle will be metric.
And its proved in Starship Users Guide v1.0, posted by SpaceX on March 2020.