No offense, but I don't see the point of this at all.
With your system, the user needs to back up an email address or other ID, a password, one or more "additional phrases", and a nonce. The loss of any one of these results in loss of their seed phrase and their coins. How is this simpler than just backing up a 12 word seed phrase which was properly generated from dev/urandom?
Either they are backing up all that information on paper, in which case they should just back up a properly generated seed phrase, or they are relying on their memory for random strings, phrases, and numbers, which puts them at a very high risk of forgetting something and locking themselves out of their coins.
Note that the "additional phrases" and the nonce is an optional values, which means that you could only generate the same seed phrases with the same email and password.
Additional phrases and the nonce could work as same as the BIP85 which enables generating multiple different seeds by a different BIP85 index.
Backup option is provided in case you forgot your email or password, or any other values you have used and it is recommended if you tend to store valuable crypto.
Same as you make a backup for credentials for other websites as well.
Of course, you could generate random phrases via the website which is generated by the browser cryptography API, and make an encrypted backup of it
https://bip39.org/#mnemonic.
That is why our website is named "bip39.org". We will add multiple tools related to the seed phrases over time.