Sure, but at the loss of the ubiquity of people capable of receiving SMS - Googling suggests ~4.5billion mobile devices worldwide, but only ~1billion Whatsapp users (a number high enough to surprise me, but still under 20% of the total potential market for SMS 2FA...)

It also introduces yet another 3rd party reliance and avenue for attack - Brazil and Turkey have blocked Whatsapp recently, and India and the UK have discussed it as well. I doubt Id want to rely on my Whatsapp 2FA tokens arriving in China either...