I understand what you mean about the kitchen being downstairs, but with this open floor plan the customers would have to walk through the kitchen and upstairs to the bar and restaurant. Just not done. Also as the attic only has two windows theres not much of a view but plenty of wall space for storage. Also what would be the point of a sunken floor in a kitchen?
As you say the only way round is a basement or an add on to the side with the kitchen in it.
I've been thinking about basements for years and it's easy to add on but as these are mostly below street level how can you stand the building with basement on a table with the rest of your street? the only thing I've seen is in some stately homes there are steps up to the first floor main entrance bypassing the ground floor which was used by servants. Or build your house on a hill 
What if they made a sort of half level where there was *just* enough room to fit a klicky...
Then made stairs leading up to the "1st" level as they did in this, the stairs would just be a bit taller.
Or they could make a fairly full basement by (as you say) putting the house on a hill.
It isn't quite as ridiculous as it may at first sound...
I could draw up some sketches if you like.
