Yep, designing around the write hole is hard, especially with non-enterprise equipment. Lots of firmware does unsafe things with cached data and will tell you data has hit disks that has not. The file system can't really do anything about this either, other than tell you after the fact that the data that should be there isn't (which ZFS is very good for).

You can disable write caches for safety, but note that this is very hard on performance.