I had a real soft spot for OpenDoc, remembering seeing the demos at AppleExpo in the late 90's.

Yes you have to start with what people need and go from there. However, you can also start from what a niche of people need and go from there.

Honestly I think OpenDoc was way too ahead of its time to be groked by mainstream users. Currently we have various workbook online apps (like Observable) that are similar in spirit and super useful to those who know how to leverage them, but haven't yet crossed into the mainstream.