Currently, we are only able to assign an Idea to one person. When the Idea touches cross functional features, being able to assign to multiple PMs (perhaps a Primary PM and Secondary PMs) would be much easier than having to use the work around of using the 'watcher' option.
I have also encountered this problem. It would be preferable for our organization to assign Ideas, next actions, and so on to a dynamic Group object (similar to workflow approval groups). If more people are added to a group, custom automation workflows do not have to be amended.