Haha sounds crazy but I've been thinking of this lately...
If an Earthbender can heat up earth enough to where it can become lava and bend lava, then perhaps an Earth/Sandbender can do the same with sand and heat it enough to where it becomes glass.
That would be a seriously tripped out ability to have. There's already Waterbending to where it can be Icebending and you can throw ice shards at someone or something to tear it up but think of how much worse glass might be. Ice will eventually melt but glass, eehh it'd be worse to get hit with that.
I'm also pondering what other possible extensions of bending there could be that hasn't been mentioned... any ideas?
Ah right, another thing that can be done with any element is flight. You can fly by using any element.