It appears the developer will have control over whether to launch the app or complete the task in the Cortana UI.
The company also singled out Uber for broad Cortana integration in a number of use cases:
By integrating with Uber, Cortana will not only recommend an Uber for you at the exact time you need it based on your schedule, but will also order it for you. For example let’s say you’ve purchased a movie ticket online and received an email confirmation. Cortana has this information and will display a reminder to you prior to the movie start time.
Google is doing something quite similar by making Now a platform for developers with an expanded range of Google Now Cards featuring third party app content. The difference here is that Cortana integration appears to be somewhat deeper. Siri lags behind the other two in its evolution.
According to an October 2014 US consumer survey by Thrive Analytics, nearly two-thirds of respondents said they use smartphone digital assistants at least weekly.
Source: Thrive Analytics, October 2014 (n=2,058)
As these services and intelligence behind them get better there will be deeper and more frequent usage. Search (as in query in a box) has limited application in a world of multiple connected devices. However a voice-enabled conversational assistant (that uses search technology in the background) is a much broader and more useful tool.
Users are much more commonly seeking direct answers or to complete tasks in using search than looking to sift through a bunch of documents that then lead them to answers or actionable choices. This is further amplified in a mobile context.
Virtual assistants such as Cortana will be increasingly oriented to “getting things done” or providing direct answers to users vs. a range of information sources or options. The implications of this emerging shift for SEO, SEM and publishers overall are profound.