After thinking about HDTV 16:9 display aspect ratio and next-generation flat panel computer monitors and digital displays, I've decided that my vote is for 2:1 aspect ratio.
This makes a for room for on-screen icon controls that do not obstruct the view of the content, and allows for hypertext annotation to movies that be displayed while the movie is running.
Since the whole object is to engage the viewer into contributing to the body of knowledge, particularly in the context of web-based streaming HDTV, the "blank space" on the side of the letterbox can become the "CRIT" space, where the fine-grained annotations can be indicated.
For average consumers, the space can be left blank, or used to display a vertical column of smaller square Picture-In-Picture iconic representations of live video feeds from other sources.
Since this is totally programmable, the iconic representations of annotions can be psychologically color coded so that they are almost unnoticable, and not a distraction; or the options could be set so that they are literal bells and whistles designed to pull you into discussion forums and video conferences related to those scenes.
Also, 2:1 is a very natural binary compliment, which will result in the most efficient use of the computer memory.
We can tell our successors in future generations, when they are watching the old movies shot on 35mm film, that in the old days before digital movie making, we used 16:9. They'll probably comment that the movies don't look wide enough!
By encouraging hyperlinking and annotation by providing a little extra space, say off to the left of the 16:9 movie frame, it will be easier to construct a "visual dictionary", with inputs from all elements of society, thus encouraging interactivity, critical thinking, and social integration and diversity.
I don't think that modifying factory production from 4:3 to 2:1 aspect ratios will be that costly, and the same flat display devices will then be able to serve both the computing and entertainment industries simultaneously.
See http://www.viewsonic.com/PROD/PANEL.HTM
These displays are being produced and sold for computers for an end-user price of under $900. It should not be too difficult to change the PC standard monitors to a 2:1 version of this item. By shifting production from this model, to one that is larger (say 2048x1024), the same item can be marketed to computer users and home entertainment users. Perhaps at a starting mass production size of 456.2mm (W) x 228.1mm (H) (18.0" x 9.0") (maybe a street price of $999 or thereabouts, to get things moving)?