The system has been designed to allow developers to easily add additional providers. I'm not sure if it has been suggested before, if not, it's worth suggesting in case others feel they could use something similar.
FWIW, as far as I'm concerned, I already authorise a number of accounts via the Authy app on my phone, and if I didn't do that, I could receive an email on my phone. I guess SMS message would be handy for people who may not have a smartphone but I would expect those to be in the minority, these days.