This doesn't seem to be a luxury method of producing general-purpose lumber, but a technique for producing special-purpose lumber. The alternative way to get similar quality lumber would seem to be logging old-growth forests, and in that light this method would certainly appear to be much more sustainable, even if it cannot satisfy all the demand for all kinds of lumber.

> ... It seems ... I doubt ... I think ...

So no real evidence.

> I won't call luxury items "sustainable"

How is wood a "luxury" item. Fruit and nut orchards both require significant man-hour and monetary effort, they would also be considered unsustainable luxuries using these rules.