Agreed. That happened in Spain: after the crisis burst the housing bubble, banks and private owner were simply not putting their property in the market to avoid price falling down. I Andalucia, the goverment actually had to pass a law that midly forced people to rent empty flats, because we were at the ridiculous situation where a lot of people were being evicted for not being able to afford rent, yet there were
lots of unused space.
So, yeah, more development might help Berlin, but it will be more effective when accompanied by rent camps and strengthening of social housing banks. Otherwise you are just feeding the bubble and exchanging one population by a wealthier one.