Well, I am not sure...

No way to toast a bowl effectively in an oven that I can figure out. Not without destroying the integrity of the bowl.

Then you introduce melted cheese, and depending on the cheese, it might disintegrate right into the soup....

Plus, remember that toasted and dried bread absorbs a lot more moisture than fresh, so by toasting the bread you're running the risk of it soaking up the soup. You would end up with a spongy mass tasting of tomato soup, which would just leak out all over your plate and be rather unappetizing.

Best to stick to the traditional sammich, I think. It's a classic for a reason.

You might be able to mix some cheeses and serve a tomato soup with a topping similar to French Onion soups... Then toast up some breadsticks, and serve the soup in a crock. That way, you have the fun of dipping the breadsticks into the cheese/soup for a little added fun. Might be a good way to use stale breadsticks, especially if you cut some texture into the crust and really let the interior soak up the cheese and soup.