Nuujinn, 
 re: is a single en-space that is twice as wide as a word space a double-space? 

 You raise the point that since Bringhurst does not talk about "double spacing" (and instead uses en-spacing which is a single character twice as wide as a word character) he isn't to be considered in discussion about whether or not "double-spacing" is "obsolete".  Your position seems to run against that of Airborne84, who said: 

  
 Airborne84 (talk)  

 I list reliable sources (all but Butterick are listed in the Sentence spacing article at this time) that either use the word obsolete, or make statements that fit one of the accepted definitions of obsolete. 

 ... 
     * Robert Bringhurst. "In the nineteenth century, which was a dark and inflationary age in typography and type design, many compositors were encouraged to stuff extra spaces between sentences. Generations of twentieth-century typists were then taught to do the same, by hitting the spacebar twice after every period. Your typing as well as your typesetting will benefit from unlearning this quaint Victorian habit." 

  
 Are you saying that Airborne84 erred when he listed Bringhurst?  Otherwise, please clarify your own statement.  Thanks, RB