With this Xcode update I noticed the following changes:

1. In the Assistant Editor, the Manual option is no longer visible. You can still achieve the same result by doing a quick open using Cmd+Shift+O then type the name of any file you want to open. Press the Alt key and the file will open in the Assistant Editor Window.

As others sites have noted the new add editor button allows you to add new editors and open files into them. You could file a bug report but you may want to consider that you're likely to get a "works as designed" type of reply.

2. When setting the size of the CollectionView, there is a new property titled "Estimate Size". This must be set to "None" or the resultant view is not what one expects.