As an indie developer I use the beta builds of Windows 10 and OSX 10.11 to confirm that my “App” will be ready and working on launch day of said operating systems. (Possibly taking advantage of new opportunities… DirectX 12 or Metal of those operating systems.) This would not be possible if my development tools did not even launch on those operating systems. As a indie developer switching from Unity3D to UE4 your comments are very troubling to me. Would a compatible UE4 version be ready/available on launch day of WIN10 and OS 10.11 or “shortly there after”?