Seems to me you can stretch and obfuscate as much as you want, but you will never solve a couple of fundamental problems:

1. The original passphrase will still have lower entropy than a sequence of random bytes.

2. The more complicated you make the passphrase->rawkey generation process, the more likely you (or the beneficiaries in your will) are to lose funds.

It's interesting proposing new ways to make a brainwallet more secure, and I get that there are some extraordinary situations where use of a brainwallet may be justified, but otherwise... wouldn't you be better off sticking with something more conventional like a paper wallet?