I was so excited that I'd found something for you that I didn't read the first part of the article carefully enough. Here's what I think based on the principles of canonicals and hreflangs as I understand them:

Since canonicals are meant to reduce confusion and duplicates, what could you do that would support that goal? If I saw multiple different versions of a product page that were essentially identical (perhaps they had different filtering options or search terms but resolved to the same content), then consolidating them all would make perfect sense. If, however, I saw two pages that had the exact same meaning but were in different languages, I would consider them as separate--you wouldn't accidentally mistake one for the other.

As for hreflangs, the second article mentioned 4 versions of the content and listed all 4 hreflangs. The idea is that the search engine could discover all the versions of the content quickly and select the right one for the searcher's language and location. I can't imagine there being a penalty for listing every one, either.

Have you had any other feedback (from outside SEOmoz)?

Google shared this post to define how to handle both issues: http://googlewebmastercentral.blogspot.com/2010/09/unifying-content-under-multilingual.html

The idea presented there is to pick the default language of the page--for most sites in the U.S. it would be English.

Then all the foreign language versions of the page should set their canonical to point to the page using the default language.

Finally, each page is to list the alternative languages with hreflang link tags.

An updated post says that ALL the languages should be listed: http://googlewebmastercentral.blogspot.com/2011/12/new-markup-for-multilingual-content.html

So I would set the canonicals to:

for all variants (in English or any other language)

and list all of the hreflang links on every page:

This would put you in compliance with Google's main post on the subject and their more recent update.

--Mike