Whoops
Yeah, I somehow concentrated on one part of the statement and missed the rest
So, to make up for it... maybe Nano will actually have higher margins than X, because while it's price will be lower, it will also get rid of the expensive cooler and the expensive power delivery circuity (just kidding).
In all seriousness, I do believe that there is a reason AMD is choosing to do this part, both on the supply and demand side. Maybe the 390X is getting hurt by the power disadvantage (demand) while AMD are getting enough dies that have all of the functional units that do not clock high (supply), and the Nano element is just an additional cherry. Maybe they simply are getting enough dies that do not clock high that it is worth the nonrecurring expenses to create a third SKU. Maybe the demand for the two existing SKUs is low enough that they want to create a third, cheaper or different SKU, but will only release it when they want to/have to move Hawaii lower on the stack.