Not really, as while you can make the domain exist you can't make the TXT record appear in DNS.

You both have to prove that you own the ability to create dns (with blogspot sorta) and the actual content. The CA provider both lists the record name and value.

You do have a good point though. I'm sure there are some services right now that allow decent control of a chosen subdomain's dns, but don't mean for you to be able to create ssl certs valid for all other subdomains too. Perhaps there should be a blacklist of sites like "blogspot". Perhaps there should be a way for a domain to indicate that wildcard certs cannot be automatically created for it without passing other conditions.

How so? You would still be subject to clicking on the link in the standard email sent to webmaster@blogspot.com to prove you owned the root.