The key thing sitting in the way of that for me, at least for the most part, is the lack of true background multitasking. I understand the need to avoid the battery problems of the Android ecosystem, but there needs to be some way to take an app and say 'yes, I really want to let this sit active indefinitely until I intentionally quit it'.

For a simple example, consider an IRC client: it's useless if it drops the connection every time you turn off the screen or switch to another app for too long.