Right, as it seems AMD is now announcing stuff that will happen in a to be released driver. So be it, AMD will later today release Radeon Software 17.9.2 For the 2 people that have been able to purchase two of them, it will bring Multi-GPU compatibility towards Vega.
AMD enables multi-GPU (mGPU) configurations with Radeon RX Vega graphics cards, releasing the new Radeon Software 17.9.2. With Radeon Software 17.9.2, gamers can pair two RX Vega 56 or two RX Vega 64 GPUs, supercharging performance and letting them play at the highest resolutions with the most detailed settings in today’s most demanding titles.
Just one example of the major impact on performance this update brings: testing done at AMD Performance Labs saw more than 80 percent faster performance using Radeon Software 17.9.2 in mGPU with Radeon RX Vega 64 in Far Cry Primal, Metro Last Night Redux, Sniper Elite 4, and The Witcher 3: Wild Hunt, over single GPU performance. We'll let you know once the driver can be downloaded, as it wasn't even released just yet.
Again let me re-itterate, this driver CANNOT be downloaded just yet.