Ability to let the public post their own tags inside of a model
I think that it would be quite useful to be able to let visitors to a model post their own tags within the model.
You would have to be able to give the client the ability to "approve" the tags that people post to their model but I don't see this as being a huge challenge.
The person doing the posting should also have to sign in with their Facebook or other social media account in order to post the tag.
I can see a lot of clients wanting the ability to engage with the visitors to their models and this would definitely give them that ability.