One thing that gets highly debated here on A.net is the appropriateness of using a given airframe on a route, whether it has too much range, too little range, too much size for the market, too small to be profitable, etc. One thing we don't have is a statistical description of what the target missions are. Of course, for a given airline the relevant routes may be a very skewed subset of the worldwide figures, but I presume for the aircraft manufacturers, they're more interested in global markets because they're wanting to sell to anyone trying to cover a mission.

I took a look around, but didn't find anybody doing this for me to look at.

I can see two ways to represent this information that strike me as being easy to grasp the appropriate magnitudes of each measure.

The first is a scatter plot where the X axis is the range required of an aircraft (accounting for reserves, headwinds, etc) and the Y axis is PDEW. Each city pair (or really, a subset of relevant ones) can then be represented as a dot. If you wanted to be adventurous, average fare could be used to draw bigger or smaller dots to indicate the value of particular markets.

The other is a simple bar or line graph with the same axis labels, but in this case the ranges would be divided into segments and then PDEW for the appropriate city pairs in that distance would be summed to indicate how many worldwide passengers needed a flight of that distance. There should probably be an additional feature to indicate number of routes used to calculate this bar, and probably the most famous or highest demand pairs within in.

Has anybody created visualizations like this or containing this information?

I searched and found the following threads, all of which were not exactly on my topic and none of which went beyond basic text tables.
Top US City Pairs (by LAXINTL Jul 21 2001 in Civil Aviation)
Busiest International Country Pairs (by Irishpower Jun 26 2009 in Civil Aviation)