I find this extension interesting, specially since its functionality can be simulated with the needed calls to glTexSubImage.
I was wondering what the advantage is of this extension? Is the rescaling function hardware accelerated or it it just a standard gluBuild2DMipmaps.
What I find weird is that it needs to be enabled using glHint? What if someone wants to disable. Why not use glEnable/glDisable on a per texture object basis?