For the sake of maintenance windows; a nice feature would be to able to unmanage nodes on a schedule. For instance; if you have a maintenance windows for server x every last saturday of the month between 2 and 3 pm, NPM would automatically put the node in unmanaged mode during this time.
This can be done today. On the server under the advanced features program folder for orion there is a Unmanage scheduling utility. Allows you to create a scheduled task to unmanage a device for a period of time. I use if for your exact example.