The trick used on old macs was pretty good: instead of a solid triangle (which can mean "pyramid" or "arrow"), use increasingly narrow or increasingly wide layers:

This means "sorted small to large":

_
___
_____
_______

This means "sorted large to small":

_______
_____
___
_

I think that would be the best solution indeed.

Would the ones in favor of "not changing" (Robert Pluim, Joost Kremers) be ok with such a change or do they still find it counter-intuitive?

I also agree that no matter what is chosen, it'd behave the same on all platforms.

Philippe