spreadsheets would be all we have.
You can program just about anything with a spreadsheet after all.
For a computer design tool page after page of spreadsheets that took coordinates, dimensions and other settings then produced a graphic of the geometry could be used. It would be a nightmare to work with, but it would do the same work as modern day CAD systems.
For a tax system, a spreadsheet that contained every possible tax form and every possible line item could be made. Except scanning through it and finding the right places to put your information would be a nightmare.
Features and benefits are nice, but interfaces are what sells. Without the right interface, there are too many mistakes, too much data entry, too many misunderstandings. However, there is a big gap between the interface of a spreadsheet being used to build a rocket, and the interface of a CAD tool. There is much less difference in the interface between Autodesk Inventor and SOLIDWORKS. Don’t find the space that has the interface the could be tweaked a tiny bit, find the space that’s still looking like it’s from an era gone by. That’s where the opportunity lies.