The breaking change this month is that apps will no longer be returned for /me/accounts and that we should not be using /me/applications/developer to get applications but this endpoint does not return access_tokens for the applications but /me/accounts does. The Graph API reference documentation does not even list /me/applications/developer so I am at a loss for how to actually replace /me/accounts as I need the access_token for applications to get insight data and other information for the application.
Does anyone know how to get an access_token for a developer's app after the breaking change?
All of these endpoints require an application access_token, how does one get one?
https://developers.facebook.com/docs/reference/fql/application
The reason you are still experiencing the "old/current" endpoint at /me/accounts and /me/applications/developer is that you must enable these changes when you are ready. On March 6th, these changes will be automatically enabled if you have not already done so. Go to your app -> edit settings -> advanced and "enable" the March 2013 changes.
As far as the REST API is concerned, you should not be building on it anymore, as it will be deprecated in the future. You should only build on the Graph API now.
If you can't find docs on the endpoint for new features, you can always use the Graph API Explorer for example responses.