I'd love to see a "there are no paths, file system is a db" like it was originally rumored Vista was going to be. I'd also love to see more opinionated OS integration e.g. per-application volume sliders, better file system search indexing, real-time built-in file and directory watching API that can be blocking or non-blocking, standardized storage of program files instead of installed app locations being ambiguous, standardized system and app settings via a neat API, etc., etc., an easy and sane git-based package manager, etc
Chrome OS has a fixed app install location, as does Windows 10 in 'S' mode (since you can only install store apps).
I remember being intrigued by the database-as-filesystem idea when it was first touted - has any OS actually implemented this? I'd be interested to see how it works in practice.
