Technology will give advertisers a completely new palate of options in 20 years. TV content will be available from many sources and targeted to niche consumer groups. Your TV will be connected to the web and able to pull programming from anywhere. You won't know where it comes from in many cases. A network? A programmer? An advertiser? All you care about is the content. Today's several hundred channels will seem small and quaint, the way our parent's 13 channels seems to us. Search engines that help us find the video content will be very powerful in terms of aggregating the eyeballs and determining what content makes it to our TVs.
On the ad agency side, art directors and copywriters will not go away, they will be more important than ever. They will create the ideas that communicate with and engage the viewing audience. Words and visuals will always be the key tools! Those who know how to manipulate them will be valuable assets. However, they will have to be skilled at story telling well beyond 30 seconds. They will tell episodic stories. They will create everything from five-second TV ads (essentially headlines to long-form, DVR-based interactive ads) to two-hour branded movies. The best branded movies will win awards at Sundance and get picked up by studios for theatrical release. Others will spawn sequels or weekly "sitcoms," virtually indistinguishable in the consumers' minds from other "non-commercial" content. A major brand might spend 50% or more of its annual budget creating a single "program"...
Media planners will not go away. Their job gets even more complicated and critical. They won't be buying nearly as many "pre-packaged" ad units, but working with the content providers (networks, programmers, etc.) to integrate their brands deep in that content. Traditional broadcast ads will persist and become valuable real estate in programs that have a high portion of live viewership (sporting events, etc.). But even "traditional" ads will change. Most viewers will have the option of interacting with them for lead generation, surveys, contests or to purchase directly from their TV.
Ad agencies that evolve beyond the :30 mold will thrive and battle with large and small studios for access to brand dollars. The weapon of choice? A great piece of video content that can do two things: entertain and effectively integrate the brand positioning.