What I think would be better, would be that app were hidden behind "views". Then the multitasking page would now list the task flows, and not anymore the apps used. A task flow would be a chained list of "views" used to get to the intented result : the task being complete. That way, you could add a new task flow, interrupting the current one, when something happens, and then be able to leave it there for some time, while switching from one flow to another. I am not sure if this is well explained, and how to do this to be usable (that's were someone like Jaakko would help a lot!). Ask me if you want to rephrase some part, or add a drawing.