Windows Phone Thoughts: ActiveSync 4.0...What Should it Be?

Let's pretend for a minute that you're the product manager for ActiveSync. No, you can't jump out the window - you're on the first floor. Ok, now if you were sitting down to design ActiveSync 4.0, what would it be? What would it include? What features would it have? Let's say that you had the option of starting over from scratch, and building a totally new sync engine, but it would mean compatibility only with the newest Pocket PC devices - would you do it? This is a completely hypothetical question of course.