I agree that taking functionality out of core into plugins is a bad approach. However, if Automattic / the gatekeepers do a good job of keeping the core clean, other projects could follow in the footsteps of buddyPress which is essentially a series of social media plugins with Wordpress MU + a theme designed to support that added functionality.

There are some very heavy weight plugins starting to come towards quite functional - PODS comes to mind - which present a more interesting set of questions about what should / should not be in the core in the future. Too much and you get bloated feature creep. Too little and it seems like the foundation has grown stale.