I don't remember ID needing a new filetype with every release in the past. A (perhaps cynical) part of me says new filetypes are designed to incentivize users to upgrade. This drive for new filetypes every year seems especially capricious when fundamental new ID features are few and far between over the past 5+ years. (Ex: one of the top billed features last year was renaming Master pages to Parent pages...)

New filetypes with every release is a source of friction to my team, especially when several users work on a project and one or more suddenly find they can no longer open the .indd project. I'm sure there are reasons for new filetypes every now and then, I just wonder if they're needed every year.