Good points — there's definitely a place for a write barrier. It may be that a simple write barrier, while not as efficient for this use case, might be generally more useful.

For your second point, if you take my initial "write B depends on the completion of write A", and extend it allow arbitrary kernel commands to depend on others, then you could still do that, (delete B depends on write A), however, things are probably too complex at this point, and a simple write barrier is better.