I would think that this would steam the outside of the bread, making it soggy instead of crisp. They make combination convention/microwave ovens that should do what you want. They also make those slightly metalized sheets that crisp things in microwaves. They're called susceptors, and they come with things such as hotpockets and pot pies. But for some inexplicable reason, nobody sells them separately. You would think they would sell them in every supermarket. It's so frustrating!

You're probably right about the soggy effect if the water heated air remained but if it was merely done to heat the surrounding air and then somehow the moisture was removed leaving the heated air behind it might work. I don't know how this might be accomplished or if it is possible.

On second thought, heat increases the capacity of air to absorb moisture.I know that a crisp crust is encouraged in baked goods by wetting them down before baking. It might require some sort of precise heat control to encourage the air to hold and absorb moisture.

I really have no idea what it would do. You could test it out pretty easily. Just put a very small container of water(maybe a shot glass) with a teaspoon of water in it it the microwave and heat it til it starts to boil. Then, try baking something along side the shot glass. I'd try it myself, but I never bake.