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.