Modern television anime is produced at an aspect ratio of 16:9 - widescreen/HD. But in the past, television anime was more often produced at an aspect ratio of 4:3 - standard definition.
When did the transition from 4:3 to 16:9 for television anime happen?
Now, it's not too difficult to find isolated examples to get a sense for when the switchover was in progress. For example, Ouran High School Host Club, from spring 2006, was produced at 4:3, while Full Metal Panic! The Second Raid, from summer 2005, was produced at 16:9. Clearly, the transition was under way by 2005, but not complete by 2006. And I'm fairly confident that by 2011, all television anime were in 16:9 (Ninja Slayer notwithstanding).
But what I'm looking for is a more holistic view of how this transition happened. Who were the major players? Can we identify a clear starting date for the transition? And so forth.