It would be nice if you could have an Ubuntu instance without root access, but with a user defined username with full root access through sudo. Just as when you install an Ubuntu server yourself.
You can just do that with a simple "adduser"
Pablo, good practice is to never use root user at all. This would save you money and year of life. I agree that these steps would help you fix it, but still it would be good not to use root from start at all. And why should DO patch ubuntu to add your key to /root/.ssh/authorized_keys instead of /home/ubuntu/.ssh/authorized_keys? This change can be done in no time at all.
You may already know this, but -- just in case -- you can disable root access yourself:
and have the added security of password-less logins:
You won't be notified about changes to this idea.