Plug and Play design

We have heard about plug and play a lot with hardware interfacing with OS, and it has taken us years to get to a point where PnP is working well enough to justify its name. What about software design? When will it reach a point of true PnP? These days a lot of people are buying into buzz words such as design patterns, MVC, etc. The more important question when you design your app is, how well can your app (or parts of it) be plugged into another app with minimal hassles? Will your app continue to function if it is loaded into another app? What happen if the path of the other app is different? Will your data files continue to load properly? If not, how do you make it so that it's easy to accommodate such changes.