Well I think we know why the iGPU would be disabled on such a part. Over the last few generations the iGPU has been the bulk of the die even on quad-core parts. Low yields are likely to affect the iGPU and the L3 cache(These two generally now make the bulk of the die area) much more often than the CPU with a dual-core part. These iGPU-less parts are likely the only parts they can produce in any reasonable quantity for the time being(I'm sure they're building up stock of what few fully-featured dies they can produce for an upcoming release).
It does mean however that any power or cost advantages there are from 10nm over 14nm are likely negated by the RX540(Polaris derived) GPU and its hungry GDDR5 memory.
At the end of the day, this die is clearly a pipe cleaner for 10nm production so they can finally start making a bit of cash back from all these dies they're having to produce to hone the node as they move towards some larger dies.