Damn that is a massive oversight. There is no sli finger on a Gtx 1060, so no traditional Nvidia Sli. There is DX12 mutli-gpu support, as dragonherder said, but no "sli".
I personally don't care just because Ive never used SLI and don't feel like spending the extra money on something that may or may not work efficiently without issues.
That being said I can see how people would care, case in point, Windows 10!!!!!! The amount of people who ARE NOT upgrading are still stuck on DX11 and won't get all the benefits of DX12, so I can see SLI being needed or wanted.
I'm no expert but this was a problem with VooDoo cards and OpenGL what over 20 years ago. I remember playing quake for the first time with a pass through VGA cable and going WOW !
We have moved so slowly ahead with all these custom tied to business X or business Y solutions and business X.
It's long since GPU hardware is an open resource to be used in Windows, OSmac, linux and VM's on the x64 platform.
I just see stupid holding stupid back myself as a Layman.
It should have been this long ago and platform independent. Vulcan has the right idea. M$ can die in a fire for all I care.