AFAIK they are changing the way 3rd party applications are integrated with FB, using a special set of user IDs for each app, and other privacy related changes which will limit the amount of user information apps get. It's a completely new system and probably tested on smaller user base than the entire FB. My guess is that it went into production worldwide today.

You are right on the money with regards to the changes, but the timeline is a bit off. All FB apps created after April 30 automatically get all the new stuff (whether they want it or not). Existing apps have April 2015 to switch to the new system. So, the outage is probably unrelated to to the new stuff.

Source: I'm a FB app developer who is seriously affected by the Login and Graph API 2.0 changes.