I agree that if there are substitutes for the app, then complexity or obscurity of the file format matters less. There are open source spreadsheet programs that

I agree that if there are substitutes for the app, then complexity or obscurity of the file format matters less. There are open source spreadsheet programs that can read xlsx format, so its not like if the Excel disappeared overnight I would not be able to access my spreadsheets. But take a less popular app with its own file format. Is it likely there will be an alternative that can process that file format? And if not, how long will it take the community to develop one? More popular app = more likely to become a standard = more likely there will be an alternative More complex file format = less likely someone could make an alternative If a file could be made readable, why wouldn't it? Relying on substitutes to address a problem you created doesn't seem fair. But if the data is intrinisically complicated (like ELF for compiled code), then there isn't much you could do anyways.