I'd be more interested in a general estimate of how healthy my lifestyle is (which is what I think people are generally, and mistakenly, using "life expectancy" as a proxy for.)
That said, any such application like this comes with pretty hardcore privacy implications. I wouldn't be comfortable giving that level of detail about my life habits to any unknown entity for any reason. An application that runs and processes everything locally and never communicates with an external server would be interesting, though!
Long answer: I would never trust my health or lifestyle data to a non-government organisation, and I would never pay for unreliable information based on guestimations.