Can only speak for myself, but since it is planned I'm focusing on the rest of my game.
Could be a while tho, so for others it may be slightly more urgent. Everything is there to do it I believe, there's a function to draw images, which can change the image, and a function to determine if the mouse clicks inside a rectangle you specify so you could do it.
I do have some code but it really needs to be rewritten if i'm going to release it. Currently i'm working on other things since image buttons are planed for irrlicht anyway. It really isn't hard to do though, just inherit the button class, provided some way for storing the image for the button and rewrite the draw function to draw the image. If people really want it i guess i could spend a little time a release some basic code.