Versioning the CC license suite will be a (the) major topic of the
summit, which will launch a long process of developing version 4.0.
All of the topics raised in the years before Wikimedia sites started
using BY-SA 3.0 as the default license (e.g., [im]moral rights,
copyleft scope, attribution, compatibility) will be explored.
Any Wikimedians are extremely welcome to attend. Whether or not in the
fullness of time Wikimedia sites move to the eventual BY-SA 4.0, it
will be at least pertinent for Commons. Summit attendee or not, if
you're interested in BY-SA 4.0 (and the rest of the CC license suite),
I encourage you to subscribe to the low volume, moderated
http://lists.ibiblio.org/mailman/listinfo/cc-licenses where further
announcements and discussion will occur.