I've been working on a patch that implements support for HTML5 multiple argument to type='file' input element. Patch introduces "#multiple" attribute to core's file and managed_file FAPI elements. File and Image fields use that to allow multiple uploads on multi-value fields. I also fixed all tests that were affected by changes in FAPI elements and implemented upgrade path for minor changes in image field's default_image configuration. Patch is ready for reviews and improvements, so I'd like to invite anyone interested to help making it RTBC.
More info:
- Issue: http://drupal.org/node/625958
- Demo env: http://d8.janezurevc.name
- Blog post: http://janezurevc.name/multi-file-uploads-drupal-8
