As long as we're looking at a wish list...
Rather than fixed gradients of altitude for texture ranges, how about using two heightfields?
If the pixel falls between top and bottom heightfield, then the texture is enabled.
If the bottom one overlaps the top, then the texture is disabled.
This would allow effects such as crustal deofmrations, shifted stratification, granite domes, etc...
In the wilds, if you see stratification in a rock layer, the bands are rarely level and normally a bit uneven. This would allow us to recreate this effect.
This would also allow us to localize climate settings to a specific part of the map.