That's the problem: if you can memorize the passphrase, it's generally easy to brute force. If you can memorize 12 words, just do that. If you want a 24 word seed, store the first twelve, then memorize the second. So far the argument has been that paraphrases are great for og Bitcoiners. That's fine, but they can figure out a way to work inside a system that doesn't burn the next billion Bitcoiners