I wish I saw this almost everywhere, and had the option for it everywhere. I am like one of those security freaks and if two-factor authentication is available, I am using it. 😛
If the option came in more softwares, would it be something you would require your users to have, or even your staff to have? Would you use it yourself?
And note, two factor authentication can be from emails or texts, or even some apps. ^.^
It doesn't really work either, just an FYI. I had it on the ACP and I was locked out so many times it's not even funny, and the support people were no help. I wouldn't use it if you ever "needed" to.
You have to consider user experience. 2FA should at MOST be available as an option, or not at all. Do not force it unless you have an authority site containing sensitive information with a high sticker price for membership - and even then it needs appropriate consideration.