If you want to get a sneak peek of what manufacturers are planning to launch in the coming years, you need only look at patent or trademark applications. Granted not everything you see will actually come to production, but more often than not there is a strong chance that you're on the right track. According to Autoguide, Mercedes-Benz has just trademarked the O-Class name in Europe, along with specific designations such as O 120, O 140, O 180, and O 200.
Historically, the O designation has been reserved for Mercedes-Benz buses, so it's highly likely that the O-Class will be some kind of people mover. That being said, the displacement figures seem a little small for a bus, and the trademark is pretty wide stretching to include cars in addition to buses. Consider the fact that the V-Class exists for people moving, and the B-Class slots in as a compact family car, and you'll be scratching your head for a while.