As a user, I'm not sure I'm impressed. On my WP8 phone, I pin a live tile to the home screen exactly where I want it, at the size I want it, and it displays the information I expect to get from it. But Google Now sounds like a live tile knockoff that's constantly changing because it's guessing what I want to see based on personal information that I agree to share with it. I don't recall this approach ever working, an…
yes, failure in the past is definitely an indication that this concept will never work.
The linked article takes a very narrow view of google now, trying to shoehorn it into windows phone terms. It's way more than a live tile. It's a homescreen widget, a lockscreen widget, an app that is a scrollable list of cards, and it integrates with notifications. Essentially, it is predictive google search - instead of having to search for something, it provides you with the results you were about to search for.
The future that you talk about for personal assistants has already been surpassed by google now.