I've been looking for something like this.  Your efforts are appreciated.  Thanks for sharing with us.

Support for imperial units would be very useful to me as 95% of the drawings I work on are done in those units.

I cannot speak for the entire CAD community in the U.S. I can only tell you what would be useful to me.

When setting elevations for slabs and floors we use decimal feet and inches.  For example 12" would be shown as 1.00' and 15" would be shown as 1.25'.  This is derived from the civil/surveying disciplines.

Architects would most likely use architectural units (feet, inches, and fraction of inches).  Examples: 1'-0", 1-3" and 1'-6 1/2".

Unfortunately most Americans never adapted to the metric system (although some segments have: scientific, medical, high-tech machining) so you'll find different variations of the imperial system amongst different disciplines. 

Spot elevations, in civil engineering, are always called out in decimal feet and inches as Cad64 has mentioned.  BUT I have a set of architectural plans for an R&D building where the floor elevations are expressed in feet and inches using architectural units.

Maybe I have the wrong impression here when the lisp routine mentioned speaks of spot elevations.  Are we talking about those used in surveying or about elevations as they pertain to the height of a floor?

After reading the initial post that started this thread I guess I'm still confused.  It refers to "spot heights".  When someone uses the word "height" I immediately think of a building.  When someone says "elevation" I immediately think of a survey, perhaps a contour map or a site plan with "spot elevations".  The nuance of speech is sometimes our worst enemy especially when we start conversing around the world with our counterparts in England, Asia, central Europe, etc.