The existing 2FA option is great for people who want to see what 2FA works like, but for those of us who really use 2FA heavily a lot of us have chosen to use a 2FA token from Yubico like the Yubikey. I’d very much like to protect my WordPress account with the practicality of the easily implemented Yubico Yubikey, which is a far superior UX to the existing 2FA option that is more tedious to use.
I am not sure there are any plans for the implementation of Yubico Yubikey currently. Since they already have invested in their own two factor authentication system, it kind of makes it an added burden to maintain another system which is used for the same purpose. So I am guessing it is very unlikely that it will be implemented.