That's cool, I hadn't played any piece that uses the stacked staff (to my recollection anyway; it's been a good 15 years since I was actively training). It does work better for when the melody progresses into that range, true, but I think it's a "right tool for the job" situation. Often 8va's are used for when you want to raise a single note or chord one time, and that would be much more readable than a separate staff or ledger lines. It seems like it's a random access vs sequential read type thing. 8va is better if you're jumping to a far octave with no intermediate context; stacked staves would be better for when the melody incrementally takes you there.

I'd love to see what the equivalents of both approaches would be in this notation.