Thanks for your question. 

Ideally I would like to design in Shaku as a unit and have either metric OR inches/feet shown as the alternate unit. 

I do understand that this might be impossible since shaku is an obscure unit as 1shaku = 10/33 meters.

I would like to avoid working with a workaround such as designing in metric and showing shaku as alternate and then make a new version of the project with dimensions annotated in both imperial inches AND shaku. 

Imperial is fractional and shaku is decimal which is another hurdle. 

Maybe working with decimal inches and shaku is easier to setup but on the printed drawing contractors really need to see fractional inches. 

A direcy way to work with inches and shaku is what I am looking for. 

So the final result is always imperial and shaku. I am used working with different units and bending my mind or conversions are the easy part it seems...