When we were kids my mum used to do this for us, but always with bought rolls. Basically she would buy crusty rolls from the bakery. Usually these would have been cooked in batches and so where they were joined to another roll there would be a bit which was not crusty. she would scoop out the bread from these points and then just pour soup into the roll. We would drink the soup from the roll, then at the end eat the whole thing. Delicious.
On the idea of making bread which was all crust, I wonder if you could do this by rolling your bread out flat, like a small pizza, then getting a potato and cutting one end flat, so it can stand on the flat end. Then wrap the bread around the potato, leaving the cut end uncovered. put it in the oven stood on the flat end and when it cooks you should get a bowl shaped bread roll that you could fill with soup.
The potato might affect the cooking of the bread though, so might not be appropriate, but a stone (hard to stand up) or half brick (square, but might work) might work better.
Not sure if having the bread around the stone will affect its cooking too much, it might be a case of try it and see. You also might not get the desired effect if the inside has a crust as well as the soup might not soak into the bread as well.
This answer will help getting the rolls to be nice and crusty I think.
I think you're misunderstanding the claim slightly. You do not heat an already pureed soup, you puree and heat in one step. You can indeed make a hot soup from cold ingredients using certain high end blenders. The only one I've verified this with is the vita-mix. To do this, you put your ingredients in to the blender, turn it on, and let it run about 5 minutes. The friction from the blades heats the soup while chopping the ingredients. The soup will get piping hot.
Why would you do it? It's easy. It takes about 2 mins to get the soup really smooth, so it's 3 more minutes to get it hot. That's faster than you would be able to do with a stove, although maybe slower than a microwave. Is it more efficient? I don't know, but I doubt the difference in electrical efficiency is really sufficient to drive a choice one way or the other.
In terms of cleaning, you already need to clean the blender because you pureed the soup. There's no additional cleaning to do if you cook it there too, versus additional cleaning for stove or microwave. And the blender is easy to clean as it's one piece; you just add soap and water and turn it on for 30 seconds, then rinse.
Personally, I do not think this is "one of the main selling points". It's a neat trick, and it's useful. However, I think that it's more interesting as an indication of the blenders power. You can use these blenders to make exceptionally smooth soup, make peanut butter, properly crush ice for frozen drinks, etc. They do this much better than a 'normal' home blender, but just saying 'better' probably wouldn't sell a lot of these things at 4x the price, so they focus on something that the standard home blender most certainly cannot do.
Best Answer
Use a vacuum pump. People who pour liquid rubber into moulds use a vacuum chamber to get the bubbles out; I've heard of people degassing wine with a vacuum pump (see these youtube videos, for example); I wouldn't know why it wouldn't work for soup.
The question is of course where you get a vacuum pump. If you're doing this in a commercial kitchen I'm sure there are channels where you can get a professional one. For the home cook (like me), one option (inspired by one of those videos) would be to pour it into a wine bottle and then use a wine saver; Vacu Vin is a well known brand. You probably won't want to fill the bottle more than half full, especially if the liquid is very thick; the bubbles in the liquid will expand a lot if you lower the pressure, and it will raise the level of the liquid.