If you all ask me:
I think Vega 12, with 1792 GCN cores, and thanks to HBM2 memory, may be actually able to be fit in Sub 75W TDP, at max. clocks.
If so, we can expect pretty high clocks from this GPU, in 35W TDP environment. I look at the Sapphire Pulse 45W TDP GPU, and it actually is 45-50W TDP GPU, with performance around GTX 1050, while being more efficient, per watt.
I think similar tricks will go to Vega Mobile, because AMD is on "killing" spree, and are investing heavily in tech they will release, thanks to money from Ryzen relases.
I would love to get GTX 1060 6GB desktop performance, from desktop GPU that will be also - fanless

. With Vega 12 it may be possible, depending on core clocks.
Vega M GL, the model with 1280 GCN cores in Intel's Canyon NUC is 20W TDP

. So I do not see any problem with Vega 12, with 1792 GCN cores, designed from the ground up to be high-clocked architecture, not be sub-75W TDP GPU.
7 nm Navi GPUs are 2H 2019. So AMD has to fill the gap with some product, till then.