That was an apology for introducing appalling latencies, not an apology
for doing things right.
I find it odd that one minute you're complaining that filesystems are
useless because problems occur if you don't fsync(), then the next moment
you're complaining that it's too slow, then the next moment you're
complaining about the precise opposite.
If you want the total guarantees you're aiming for, write an FS atop a
relational database. You *will* experience an enormous slowdown. This is
why all such filesystems (and there have been a few) have tanked: crashes
are rare enough that basically everyone is willing to trade off the chance
of a little rare corruption against a huge speedup all the time. (I can't
remember the time I last had massive filesystem corruption due to power
loss or system crashes. I've had filesystem corruption due to buggy drive
firmware, and filesystem corruption due to electrical storms... but
neither of these would be cured by your magic all-consistent filesystem,
because in both cases the drive wasn't writing what it was asked to write.
And *that* is more common than the sort of thing you're agonizing over. In
fact it seems to be getting more common all the time.)