Don't think that design is anything official. The buildings that will be depicted on the coins are already known indeed, even for the last pieces in that series: Wartburg (Eisenach) for Thuringia 2020, Sanssouci Castle (Potsdam) for Brandenburg 2021 ...
As for when the "look" is decided upon, well, the designs of the 2007-2009 coins were chosen in April 2006. Maybe the jury does something like that next year too, I have no idea. What we do know is that the Bremen coin will depict the Rathaus (city hall and state parliament) and the "Roland" statue. But what the coin will actually look like is not known yet.
Christian