@XPM
That analysis assumes that the designer is stupid enough to scale the entire aircraft down by a fixed ratio.
If the weight did indeed scale by [L]^3 - which i in fact doubt - then since wing area is definitely scaling by [L]^2 you'd end up with an aircraft with 1/10 the wing loading. That alone makes any further attempt to extrapolate the deign pointless.
It also assumes the designer, having been stupid enough to scale the whole aircraft, then ignores the drag of HIS aircraft and just scales the engine too. No-one does that either.
There probably aren't many aircraft at 1/10 the size of the A380 - but there's a whole class of medium sized business jets - such as the Lear45 to pick one example - which happily and successful fly around and are about 1/5th the size of a A-380, and they definitely are not restricted to propellor-class performance.
There ARE economic advantages of scale, to be sure - but to extrapolate from that to saying small aircraft "don't work" is a great deal of a leap.