PNG with selective color-palette

[MasterFX]

Hello.
I'm using the PNG-Format frequently for desktop screenshots. In most picture editing programs there is a function "selective" for the color-palette. This is really cool, because with that function you can reduce the filesize as much as possible but keep the important colors of the image. Unfortunately XnView don't have this function and so I have to use more colors, e.g. 128 colors instead of 32 to keep the image viewable.
Is there any planning to include this function in XnView?