This etude is nothing about hand span. This etude is an etude of pure dexterity and suppleness. The key is the contractions. People focus on the expansion, but really there is none. (At least in the technique I have adopted). I always keep the wrist low, fingers pointing slighty towwards the right FLAT (that is a major issue) and let the thumb follow the hand and come down. This eliminates all isues on hand span, as they all become easy like this.
Has anybody used the fingering 1 3(or2) 5 2 1 3 5 2 .....
Cortot used it. I have practiced it like that a lot, and it is very good, alhough I would never perform it like that, it really shows you the correct movements if you can get the thumb over the 5th finger perfectly legato. It forces the hand to do the correct movements and and if perfectied it can be used in performance.