Hi Marius,
From a core Moodle perspective, this would be an improvement and therefore would go into the next version, currently 2.7. But that would depend on how long it took to add and if there was sufficient votes on the tracker (if there is one or one to be created).
Therefore with those time and version constraints you are better off requesting / working with the developers of the block manager (https://moodle.org/plugins/view.php?plugin=block_cmanager) to iron out the bugs and add in the features you require. I had a quick look at the code and there is a separate database table where new options have already been added. And block do support storage of files - http://docs.moodle.org/dev/File_API#File_areas - however, I do know from the grid format that file upload and storage is not simple. Despite all of this, the contributed solution will be the fastest option, even if you fork the code and perform the work yourself. The source code is after all GPLv3 as with all code and plugins in Moodle, so you can copy and improve on it.
Cheers,
Gareth