Add support for FIDO U2F hardware keys.
Because FIDO U2F uses digital signature that makes this technology even more safer than the One-Time Password, because you only need to store the public key... and even if someone gets the database with the public key it wont help log in unless the public key technology becomes broken in the future (it can happen, but still more safer).
By all means keep the One-Time Password! I personally use it and I think is fantastic! Just add the FIDO U2F as one more option available to make the account at hover even more secure!