Why only 50% of the ad spend? I think the article makes the case that all ad spend is moving to digital. Probably not ever reaching 100% but a lot closer to 100 than to 50.
Also look at the linked graph from the 1.29% article: http://images.bwbx.io/cms/2014-02-28/ADS_medium_share2.jpg
Each generation of advertising takes over more, but magazine, radio, are remarkably robust. TV will remain too (even if some transfers to Hulu/Netflix/etc...).
That's mostly due to the explosive growth of mobile, which it seems that graph leaves out.