Regarding the question of whether Google is a monopoly or not: non-monopolies cannot easily cause a new Internet standard to spring into being simply by announcing that a program of theirs will now apply specified behavior to a previously undefined syntactical element.<p>This line has a whole lot of chutzpah:<p>"This <i>standard</i> can be adopted by any search engine when crawling and indexing your site."<p>[Edit: Incidentally, I will have this implemented on my site by the end of the day. Because I'd be an idiot not to. Google is, I think, probably the only company who can create "drop what you are doing, now, this is your new priority" work for me besides my <i>actual employer</i>.]
You are much better off with doing the following: (1) All responses for non-canonical URLs are 301 redirects to the canonical URLs, (2) Your website will never link to a resource using a URL other than its canonical one, (3) you encourage people to link to pages on your site using the canonical URLs.<p>This way your site will be very cache-friendly while still being usable. Also, all search engines will be able to understand your site without any proprietary extensions (a.k.a. "standards" at Google, apparently) being needed.
Why didn't they use the already established rel=bookmark value from the hAtom microformat? That's already in the wild on countless blogs and websites.<p>I swear, sometimes Google's awareness of existing web conventions is <i>shockingly</i> lacking.
(Black hat on) This might be very interesting for some types of injection attacks. Instead of simply getting backlinks you could steal the pagerank of your victims without leaving a visible mark. Limited to subdomains, though.