I will clarify things a bit
Lisa Su in July have said that Vega architecture comes within two upcoming quarters. She meant: Q4 and Q1 2017.
Then we have investor slides where there is information that Vega for Enthusiast market is coming 1H 2017.
Next are information from VideoCardz, FUDZilla, and WCCFtech, that Vega 10 is coming this year, for professional market, and Vega 11 will replace Polaris in professional/server market by next year.
What all of this means?
Vega 11 - RX 490 - high-end market is coming this year.
Vega 10 - Enthusiast GPU is coming this year, for professional usage, with Enthusiast availability in consumer space next year.
For me, the only place where Vega 10 could appear this year is Mac Pro. Its small volume enough to produce enough chips(we are talking about 30k computers shipped this year - 60000 GPUs). Vega 11? Possibly, as the base model, or in the middle.
Also keep in mind that The GPUs will be very high clocked. Consumer parts can clock as high as 1.75 GHz stock, with Server/professional ones clocked at 1.5 GHz. So there is plenty of room for undervolting and saving the power from thermal envelope on the GPUs.
4096 GCN core chip, made on process that is not letting down the microarchitecture, with 1.25 GHz giving 10.240 TFLOPs of compute power.
3072 GCN core chip made on the same process with 1.25 GHz will give 7.68 TFLOPs of compute power.