Many people here mix miles and km. For the over 50 crowd, we learned miles, feet, and pounds, etc. in school. We get a lot of US television and movies, so miles, feet, and pounds, etc., so we see and hear it constantly. Gas mileage is used more than litres per 100 km. At least, around where I live.
In grocery store flyers, it's cheaper to advertise in lb, instead of kg. Would you rather pay $1.49/lb or $3.29/kg for hamburger?
The law says advertisers must use kgs, litres etc. but many flyers have lb in bigger type than their metric equivalents. Gas is exclusively advertised in litres, but other fluids are a mix of metric and Imperial.
Justin Trudeau's father, Pierre, started it. I don't know how many more years it will take before we have completely switched over, but having you next door has slowed the conversion.
It's like speaking two languages and being fluent in both. I don't see any problems with it.