The Ad Component is a very big step in the right direction but the focus there is more on managing the advertiser / client relationship with the outgoing and incoming ad acceptance features. We need something similar for internal use, And the ability to have multiple playlists - not just the global one. I would like to have a separate playlist for each zone/region in a timeline per campaigns. Each playlist would rotate through resources independently of the other. I would schedule all of these resources in an easy-to-administer list view that would let me choose start/end date, days of week and times of day per resource - per playlist. When you add the ability to have transitions between resources, you could program that in the list view as well.
The main timeline metaphor would still have its place for overall programming. I can see scheduling additional resources in the timeline such as weather, rss - following a playlist component. This would give us great control over the balance of how things played out. (although these resources should be able to be nested inside the playlist component as well).
You have a great system and I don't want to sound negative. This feature would just add an enormous amount of additional programming flexibility.