> Have either database-like transactions or (at a minimum) write barriers for file operations.

Go one step further and have the kernel expose a much more structured view of storage to user space by default. 99.9% of user space programs I've written don't want to deal with file IO, they want a database, or some other way for arbitrary in memory objects to be persisted and shared between processes. There's so much room to improve on the 1970s era IO primitives we use by default.