Update: Plans in Drupal-land have shifted towards Create accessible markup for a drag & drop file upload widget (and ensure there is an accessible alternative interaction) and the original issue slated for D8 has been closed in the meantime.
Original request
This is a follow-up to #1380, the respective issue for https://www.drupal.org/node/2113931 and part of #779
Here's what they ~are~ were aiming for in D8:

GitHub Issue #:
1445
Recent comments
@themetman Good to hear your solution. May be helpful for others in the future.
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