v4 is indeed BDW.
It's supposed to be out in Q1, which is almost over.
I'm not sure Vega 10 was postponed because of Radeon Pro (to give it some time in the market before Vega based cards take the crown again), or if indeed it's related to yields and cost. Probably a bit of both.
Vega in 2017 makes it weird for Apple not to have it as a high end option on the nMP, or maybe they'll just release the lower end parts now and a higher end one next year, but unlikely.
If it comes out this year, GPUs will be all GDDR5X based most likely.
Still, there is no complete lineup, Polaris 10 for D310, Vega 10 should be for D510 and D710, following the current setup.
[doublepost=1458076246][/doublepost]Probably is, we just lack official announcement.