Parametric modeling is not a cool trick to have at hand, it's a way of life !
Having a way to share parameters across referenced models would allow much more flexibility in complex designs hierarchies ... maybe through an imported "sketch/data only" file .. or better by including ALL (local AND imported) components in the model parameters tree.
It looks it has been discussed as "imminent" in 2015 but still ... waiting for this in 2018
https://forums.autodesk.com/t5/fusion-360-design-validate/linking-parameters-between-parts/td-p/5641...