Hi Remko, your request is certainly high on the list of priorities.
In order to get this implemented we need to resolve a few issues first as well as carefully think about what needs to happen to support this properly: image you've created a folder with a typo in it's name, you also want to be able to correct directly from the Fonto UI. Renaming an existing folder may break the existing references in your content, so we need to make sure we take that into account as well.
We will keep you updated on the progress of this feature request. In the mean time, please keep reporting your ideas so we can improve our product!