Idea portal and promoting an idea to a feature is great great great thing ... however, there are times when features sit in the parking lot long enough and don't move forward and I would then like to demote the feature back to an idea to see if anybody is still interested in it.
You can do this today. Choose "Create related idea" from the "Actions" menu for the feature. This will make an idea and link it to the feature. If you no longer want the feature (e.g. to completely demote it) you can delete the feature.