I saw this thread after I posed my new version announcement for FlexUnits.jl which includes this feature. It simplifies units better than upreferred which can give you rather opaque results with a lot of electrical units. You can even use display_simplified_units(true) to set it to simplify units by default when displaying.
FlexUnits.jl follows much of Unitful’s convention so it shouldn’t be too difficult for most people to pick up. It matches Unitful for speed in statically inferrable cases, but absolutely dominates Unitful for cases where units can’t be inferred (this bothered me a lot because I often build configurable systems where I have to parse units as string, which completely wrecks performance, FlexUnits solves that problem with Unitful as well as many others).