Thinking about this a bit more, there are a few options for single-file exports:
1. Always show the rename field in the config screen. This will force the config screen to be shown even when there's no other config.
2. Only show it if there's already export config.
3. Allow the plugin to decide whether to show it or not. This hooks into
MDL-16414 - where I was thinking perhaps about letting the plugins be able to say that the confirmation screen shouldn't be shown if it only consists of information about previous exports (this is for the download plugin)
I want to find the right balance between convenience of being able to rename a file, against making the export as quick as it can be. For example right now most of the exports to mahara go straight through with no extra screens and I wouldn't want to add a 'rename' screen in there, I can rename it in the remote system later, and it already goes into an 'incoming' folder that I want to move it out of. Forcing a whole new screen here wouldn't work in that situation.