Force inside a cylinder vessel is just pressure times surface area. If you have the same pressure(soda carbonation) with more surface area, then you are putting less force on the walls. I don’t have any specialty in the materials engineering for canning, but i suppose less force on the walls means you could use thinner materials. However, soda can walls are already pretty thin to start with and from what I can find online, the tops are usually 2.5-3 times thicker. So, I could see it potentially cutting some cost from the tops by making them thinner but i doubt they are manufacturing different tops. It’s probably just marketing.
“Official capacity” has not been defined yet so we don’t know what the limits are. We will have to wait and see.