In the current Linux drivers of AMD you can find first indications for a graphics card with two GPUs of the Vega generation.
The latest AMD drivers for the Linux open source operating system suggest that AMD is working on a high-end graphics card with two Vega GPUs. Concrete notes provide information on a fan controller which is designed for more than one chip. The cooling will seem to be an AiO-water cooling, which has to cool besides two graphic chips also a PLX chip for the data exchange between the GPUs. By using a PLX chip the graphics card with two GPUs should not be braked by the bus with the connection of a maximum of 16 PCI Express 3.0 lanes.
With a dual GPU, AMD with the Vega generation could still outperform the currently most powerful GTX 1080 Ti from Nvidia. Current benchmarks of a graphics card with Vega GPU suggest that the new models of the next generation can barely match the current Nvidia graphics cards.