I still dont get what Vega is even going to be. Just one GPU(with two models) at the very high end(>GTX1080)? There's supposed to be a 2nd Vega, but they aren't talking about it, and from what they keep making it sound like, in terms of the general desktop market, there's only RX Vega. Is the other some lower power laptop chip or something? Maybe a dedicated professional card?
Thing is, if Vega is just one GPU, they are leaving too much ground uncovered whatever they do. They either aim high for the 1080/1080Ti-level market and compete there and completely leave open a huge gap between the 580 and Vega where Nvidia will continue to reap in that lucrative market with the GTX1070. Or AMD do something more towards the 1070/1080, which probably has bigger reach, but again leaves them without a flagship product, keeping them looking like a budget brand - which they said they didn't want to do.
I cant imagine they would simply do a massively cut down Vega to cover both bases. For all the improvements they'd likely get in yields, that'd probably still end up being a waste of an expensive, high performance chip.