The only way for VR SLI to ever become a reality will require UE4 to implement it. Should I abandon my 2 980’s and just buy a 1080?
I doubt you are going to see Epic put it into UE4. You will have better luck with Nvidia doing there own branch of UE4 with support like they do with gameworks. The reason I say that is that Epic has been very upfront that they are netural in that they won’t support Nvidia over AMD and vica versa. If they tech can not work for both with equal performance then I doubt you will see it added in.
I have 2 780’s and I would love to see VR Sli added in. But I have all but given up on that hope. I bet Nvidia is working on a branch of UE4 that has support in it but who knows how far out that is down the road.
If we ever get DX12 Multiadapter support (pipe dream) that would go along ways to providing a similar result I would imagine.
AMD does have Liquid VR to balance performance.
What Unreal says here is that it’s just really hard to figure out how to put it in Virtual Reality Updates in 4.11 | Feature Highlight | Unreal Engine - YouTube
But, I still think you are right and should be looking to sell my cards as fast possible 
I’ve been wondering the same thing…it’s been over 6 months since that Nvidia announcement. Have you guys used any of the gamworks stuff?