The basic idea would be to give each device a shard automatically (but allow it to be overridden) and then be able to set a release schedule for profiles and applications.
For example, on the assign page for a profile, you could select "Shard this assignment" and then be able to select 7 days and have the profile released to (total devices / 7) on each day. Would also need the ability to stop the rollout.
We currently do this in our internal munki with an installable_condition.