1. Remove the ability to save workbooks. This would keep the excel in organisations where it excels (pun intended), namely quick & dirty sketches and visualizations. If you need something twice, it is likely you need that more than twice and you should be using something else.
2. If not that, give me a worksheet type that forces each cell in a column to have same formula or data type. and just a sheet that you can refer to as any other sheet, not a powerwhantnotthingy.
3. Version control. Seriously, Microsoft, what on earth are you paying your excel developers for if not this?