What you are talking about is unrelated to NFSs broken model. Although still important, because these are the reasons why we don't need fsync() to actually flus

What you are talking about is unrelated to NFSs broken model. Although still important, because these are the reasons why we don't need fsync() to actually flush data to disk for example, it can be asynchronous and only needs to add a checkpoint to your log structured filesystem that will be written to disk later, once enough data is buffered or long enough time has passed.