Microsoft was asking that write barriers be added to SATA just three years ago. I don't know if they made any progress. There are several related patents and patent applications out there.
Hitachi, for example, has a patent on transforming a flush cache command into a write barrier in a disk drive, something that is necessary (more or less) to implement an asynchronous cache flush (cf. Patent 7574565, filed 2006, published last year).