UploadWizard has a feature specific to Wikimedia Commons where it checks whether the uploaded file has the STL extension. In such case, an additional dialog is displayed asking the user for patent rights and afterwards, a warning is issued about uploading weapon schematics. This was removed in MediaUploader (see patch).

This is an example of a type of feature that could potentially be useful to other parties – displaying an additional dialog if some condition is met. MediaUploader could provide a hook interface for that.

I currently have no specific use in mind, so I'm leaving it here. We can discuss this idea further if the need arises.