Yeah I've already tried to upload w/e file (even script file) type through CSS property or Image and it's working, but I don't think it will fit my needs.
To explain a bit more, I want to offer this upload (if possible) so for example a designer can use its own .json file to pre-fill custom component properties. For the moment I succeeded doing it only because the .json file is on another server, and the designer has to enter the correct URL in a property.
Uploading it through CSS or Image seems like it not possible to give me back the URL it was uploaded to, so I can't retrieve it from AJAX for example.
Do you known if this could be possible in any way 
?
Br,
Vincent