Ask Metro’s trip planner to plot a journey from anywhere in Rainier Valley (south of Alaska Street) to Southcenter Mall and the results will almost always show a trip that takes roughly one hour and requires more than a quarter mile of walking. If your starting location isn’t near one of the light rail stations, your journey will always require 2 transfers (usually the unreliable 8 > Link > 128 or F). When you arrive at Southcenter, you will also be dropped at a location that may be far from your ultimate destination inside the mall and you will have to navigate through a parking lot that is not well lit in winter or in any way pedestrian-friendly during any season. Most automobile trips between Rainier Valley and Southcenter will take 15-20 minutes and, on most days, you will be able to park close to your destination in the mall. Of course, at the height of Christmas rush, in a singly-occupied vehicle under miserable weather conditions, your auto trip may take longer than 20 minutes, but your transit trip will also be lengthened under those conditions, too. One of my teen-aged neighbors worked at Southcenter during the Christmas retail season and she had to make that 60+ minute trip twice a day, often returning home late at night after making 2 connections, sometimes in very bad weather conditions. How could her trip have been more convenient and quicker?
It might be possible to extend route 156 to Rainier Beach from Southcenter. The frequency and span-of-service provided by the current 156 would likely match the demand for service between Rainier Beach and Southcenter. The extended 156 would need to serve Rainier Beach Station and provide a connection to route 7. Metro could also extend the 156 to serve the Prentice loop and then terminate every route 7 trip at Rainier Beach. Extending the 156 to Prentice Street would also provide a direct connection to the Rainier Beach Link Station that might help to revive ridership on the Prentice loop.
For a few years, Metro extended old route 39 (Seward Park) to Southcenter between about 9am and about 6pm. But that was before Link was built and the 39 had few riders. Today, Southcenter has become much more of a destination since the days of the 39 service and the city of Tukwila is making plans to create a walkable and more active neighborhood in the area surrounding the Southcenter mall. I think a direct bus between Rainier Valley and Southcenter would attract many more riders in 2015 than the 39 extension did in the early 1990s. But the current service that relies on an unreliable route (8), requires 2 transfers and can take 60+ minutes when everything goes right isn’t going to attract many riders.