There is already a feature to do this in the Ingest dialog. It is a checkbox titled "Unmount Source Disk(s) after Ingest".
I found it just today. It is great to know you still usually develop a step ahead of user requests but sometimes makes me feel a foul with the requests...
,-))
There is also an "Unmount" button in the Ingest dialog that will allow you to unmount a disk if you don't want it mounted anymore.
This one I didn't find either. I was looking for the usual eject sign and didn't notice the unmount button.
But I still would find it useful to add an unmout button to the Ingest progress window in case an ingest is complete to be able to manually remove the not needed drive. But I think what there is can be used for good.
Thanks a lot!