I am really surprised by the collective refusal of brain wallets. It all started roughly two years ago when suddenly a secret society of crypto guys started a war on brain wallets ... including popular ones like brainwallet.org that I have used thoroughly back then.
I guess it would be sufficient to just clearly state that the "passphrase" has to be unique and not "guessable" by anyone else, but that would be just to simple, wouldn't it?

I have personally lost BTC, that were stored in my mobile wallet (when my mobile was "borrowed" by a worthless asshat in the subway).
I have lost BTC that were stored in a wallet.dat when my SSD suddenly failed.
I have lost BTC that were stored in a wallet.dat when I accidently typed rm -rf / into the console.
But I am yet to lose any of my BTC that I have stored in a brain wallet.

People have tried to convince me to store it in an online wallet (where the owner may pull of Houdini's magic disappearence act anytime) or on a crappy 100$ SSD (which failure is a poisson distribution around it's END-OF-LIFETIME point) before, but that's not gonna happen!

Saying "all brainwallets will be emptied" is just as wrong as claiming that "alternative storage methods" are fool-proof.