It's not so simple, if you look from first principles. It will always depend on the cost of communicating versus the benefits of economies of scale in computing. Currently, most many can only be done in the cloud due to the massive scale benefits and relatively low communication costs. If communicating doesn't get cheaper but smartphones get massively more powerful and roomy overnight this might change; but it is a fact of computer science that there are economies of scale to lumping queries from different users.