This is an interesting approach, but I see one flaw: If this sort of technique be comes common, wouldn't an attacker just need to know what word list you 'rolled' your password on and then can just brute force all the password combinations from that list?
Example, pretend that you had to pick a password for a new website that only allows all uppercase English characters, with no numbers or symbols allowed (just to keep the math simple). A normal ten character password gives an attacker 26^10 possibilities to try.
Your lets say that your diceware generated password picks 6 words from a list of 1000 words, and each word is 4 characters in length. If you skip white space, conventional wisdom would say that your password is 26^24 possibilities to guess via brute force.
But because this has become a common trend in password generation, or because the attacker is the NSA and have been watching what you read, they know you used this list. They don't bother to try all the combinations, just all the combinations of the words on this list. This gives them only 1000^4 possibilities to try. As it happens (yeah, my example is rigged), this is exactly 1 trillion possibilities, which if they were guessing at the rate suggested in TFA, would take them exactly one second to break via brute force.
Essentially, you are replacing individual characters with words to make a long password easier to recall. There is no reason why an attacker cannot do the same thing, mapping one 'alphabet' of symbols onto another.
Now, some people might point out that there are some things you can do to mix things up a bit and force an attacker to have to dig deeper, but my point is that this might actually make it much simpler for a smart/informed attacker to brute force a password.
