The majority/all of the changes to the AddOn API have already been released during the Legion Pre-Patch 7.0.3 on the 19th of July. If you are just coming back to WoW make sure to check out our awesome updater called Minion. Update all of your AddOns from WoWInterface with a single button click and even enable automatic updating.
We have renamed the pre-patch compatibility tag for Legion. It’s also a good time to check out our update API and integrate uploading to WoWInterface in your release scripts. Those coming back to WoW and have questions about Legion AddOn changes please feel free to post in our forums or join the party in IRC.