SGIS_generate_mipmap in or out?

I saw in 3DLabs papers that they weren’t sure whether they had to implement this extension in OGL2 or not.

My question: tell me one reason not to implement it?
This extension has plenty of advantage I’m not going to debate now, but I don’t see the disadvantage of putting in OpenGL 2.0.

It could be a new state of the texture object?