If the overwhelming majority of the population favour a socialist system. Society is already largely organised as a planned economy then a peaceful transition is perfectly possible.
No one needs to be killed. Why base future predictions of change on events from the past when socialism and democracy were not as developed?
The present economy might well be largely planned, but I don't see how it can be assumed that a majority of the population will some day favour a socialist system. In my experience, the views of most people are a mish-mash and they are, in the end, easily swayed by the dominant ideas currently disseminated by the mass media. These ideas will never favour socialism.