Just installed a fresh install of 4.16.1 on MacBook Pro.
When I click the yellow Launch button, the screen minimizes, then if I maximize it, the button has changed to Please Wait which stays there for a few seconds and then it just goes back to being the Launch button again.
I was able to workaround this by checking the logs in Saved\Logs and found that UnrealHeaderTool, and ShaderCompileWorker were not built when I built using the scheme UE4 - My Mac. So I built those other projects in XCode, and was able to get the editor launching.