I would want a "zoned spreadsheet", where you can define a zone grid on each page; each row and column of the zone grid defines the number of rows and columns of data in that zone row/column as well as names for rows and columns, and each cell of the zone grid (which is named by the combination of the row zone name and column zone name) has properties such as formatting, protection, default values, etc. Formulas can go in zone cells and in data cells (although if a zone cell contains a formula, then the data cells in that zone will have the data automatically filled in and you cannot change it without removing the formula from the zone).

Another thing I wanted is to be able to write extensions in C, and to work with non-Unicode text.