The least square regression of the power law and the quantile regression give similar results for the 50 % quantile and also the support line at the bottom. @TheRealPlanC 
 
I think that is the more robust result. 

The support is even more convincing and logically consistent.

The interpretation of the top quantiles is really problematic because it implies there are multiple slope power laws that makes no logical sense (besides being "close enough" to the other power laws even including more and more bubble data).

It is true that the importance of the bubbles is decreasing but this is not going to make the top lines parallel to the middle line. They will continue to deviate mostly because of the contributions of the early bubbles. 

So if the quantile regression was used mostly to find an equivalent to the bottom, so in other words a top channel, I think it doesn't do that at all. It is a good result in terms of showing that different types of regression give similar results. 

In other words it is a power law no matter how you slice it. 

But I'm I don't think that the right interpretation of these top lines is that they give us some meaningful boundaries for the top price.