Around the time the malls came to Sofia, the municipality also started renovating the main streets in the city center turning Vitoshka into a real pedestrian street and building proper sidewalks on others (like Shisman). The renovations are still going on (Solunska, Graf Ignatiev) and this will only accelerate the process of turning the city center into a recreational area. It's really nice to see how new restaurants, bars, juice bars, soup places, sandwich places, and cafes pop up on streets just months after they have been renovated.
Other factors accelerating the process has been the large expansion of the metro, which happened at the same time as the malls were being being built, the renovation of tram tracks, purchase of decent trams, and the almost complete replacement of the old city buses with modern ones, all of which has given people from the neighborhoods easier access to the city center (which has never been very accessible by car).
Sofia is slowly becoming a modern metropolis.