That exact strategy is described in the second paragraph but the author argues (and I agree) that it is so arduous it will cause you to lose many users for questionable benefit.
Yes but the exact quote is confusing as he specifically mentions email addresses (in bold text). I know the author mentions usernames elsewhere in the article and I agree with the author this isn't applicable to websites that allow username signup since anyone can pick any random string... But for email address signup, as the exact quote mentions, there is no additional context switching since you already need to confirm the email address regardless.
Sure, companies are free to make their own choices based on their business incentives. But if you can create an account and be logged in without verifying an email address, then arguably the email address wasn't needed in the first place and you should just allow any type of username string. If the goal of your website is for email address to be the username, the you should confirm the user actually owns the email address they claim first - since anyone could lie and put a random email they don't own.
