If you absolutely MUST use a brain wallet, why not make something that takes Armory's master key and provides multiple methods of representing it as easily memorizable words or phrases? You at least keep Armory's crypto-securely-generated master key. You don't make it any less of a risk to forget it, but it's a step up at least.
The main reason - Armory's master key generated by Armory's algorithm. If the algorithm will be compromised, or will be picked up initial conditions for key generating, then your coins will be at stake. In addition, I think it is not easy to find out (and remember) a phrase for existing key.
I just like idea that you may use your favorite phrase to restore wallet anywhere anytime. Just select strong passphrase. In addition you may create paper fragmented backup if you like.