It is widely rumored that the next A-Class will be available as a 4 door sedan, as well as the regular 5 door hatchback. Mercedes is thinking about the US market for the sedan. Just like Audi is with the next A3. Which will also come as a sedan as well as a hatch.
But the small Mercedes sedan might actually be more like a compact CLS than a regular sedan. What they call, wrongly, a 4 door coupe.