This would be a beginner session for those who are familiar with Drupal 7 but haven't spent much time with Drupal 8 yet. What's new? What's cool? What's possible with core now?
I won't talk about about aspects which have a session on their own (like Twig).

I'm not really sure how many people are interested in a session like this. Maybe everybody is already fmiliar with D8? If the session happens it will best be placed as one of the first sessions Saturday morning.