Something that's held me off upgrading the allotment website from Drupal 7 to Drupal 8 has been the media handling capabilities. Whilst Drupal 7, out of the box, didn't have good media handling -- and by media, I'm mostly meaning images -- with a number of modules I'd created something that "mostly worked" albeit with a slightly awkward workflow.
In Drupal 7 I've had the ability to drag-and-drop images onto an article, page or blog node, and then click to insert them into the body text, selecting a filter to set size & aspect ratio. When viewing the article, the images could be clicked and they'd zoom to the original size.
Getting most (or all) of the functionality I had in Drupal 7 replicated in Drupal 8 is a key requirement to migrating - and was one of the main reasons I aborted upgrading earlier in the year.
Back in the spring & early summer, I found that the Drupal 8 roadmap looked to have most of what I was needing scheduled in 8.6 * 8.7... So, now that 8.6 is out, it's time to start again...
At the same time, I reckon its finally time to move my own Drupal 6 site to Drupal 8 - and make it an ideal testing ground!