Raja said so back at CES 2017 but as you see in this discussion, technical subjects are brushed under the carpet.
So he said
a) that a Ryzen CPU + Vega GPU will build an ecosystem, for greater performance combined than each part on it's own.
b) multiple Vega CARDS will be seen and working as a single entity in the system.
c) the HBM Ram on the Vega Cards, is actually Cache, and it will be used as such by the other AMD parts in the system.
However most here thing that ( a ) and ( c ) cannot be done, even if Ryzen is SOC CPU and actually has direct access to the GPU.
And still confuse the ( b ) with Crossfire even if AMD is strapping 4 CPUs on the same PCB and selling them as single CPU because of the infinity fabric. Something that up to now couldn't be done.