Based on what I've seen elsewhere in Germany, Berlin will start seeing lots of empty apartments now that it is too much of a gamble whether you'll earn profit renting (since Germany's laws protect the renter more than the landlord, which you can combat with a portfolio of properties that earn a certain level of rent to cover the non-paying tenant that you can't evict), and because there isn't much of a good reason to sell (maybe in a few years things improve, or maybe the apartment is useful for family, or one's own future retirement home).
