> This is almost trivial: use a PasteUpMorph with grid layout,

A Table Layout wouldn't work; but what's a "grid layout?"

> plus a method
> telling which submorph is located at a specific coordinate, and you have it.

You make it sound like it's one evening's work, but what I want would
take a lot more than that.  Besides everything I already said, I want
something that looks and feels like a standard spreadsheet, with a
cell-cursor, arrow and page movement, resizable columns, etc.

I would feel compelled to develop a custom SpreadsheetMorph with its
own layout and drawOn: to accomplish this..

> The drag and drop stuff can be implemented by populating the spreadsheet
> with initial empty cell which, upon a drop event, becomeForward: the dropped
> morph (possibly resizing it); I have done this in muO's musical graph
> system.