He does at least put down Tutorial D as an alternative to SQL, which is Chris Date's relational language.
The issue is not the relational model, which is pretty simple and powerful. The issue is that SQL reflects a more complicated multi-set multi-valued logical model.
Why not indeed. Many times all that is required is a few files written to /tmp atomically mv'd in place. Also, see git's design[0] and how it makes operations like fetch/push completely trivial. Also, how redis reliably dumps and appends.
Sure, why not?