What can't you do in Excel?
thorax: Best ideas I have here:* Support Seadragon-like zooming into cells which expand into full spreadsheets of their own. You can go to infinite distance deep into the spreadsheets and each spreadsheet chooses a "cell" value to represent it to above container sheets.* Ideally the above spreadsheet allows you to pull in other people's spreadsheets across the world to use as one of your cells (somewhat like Yahoo Pipes, I suppose)* Alternatively, I'd like to see Excel go three dimensional for a single sheet. At a minimum perhaps use "layers" like Photoshop would to apply transformations and adaptations that collapse into the final view.* I'd prefer this imaginary Excel also use Python or JavaScript for cell programming/calculations.* I second the versioning information idea, too-- keep a history of every manual change to every cell and allow them to be reverted. In a git-esque way, support branching of cells, etc.