There was talk of using a very small amount of HBM1/2 as cache (128/256MB or similar) which could help, and if its small, it may keep the cost impact down. Something small like that may keep the pricing much more reasonable. I also seem to remember around October time, Hynix IIRC was going to start offering HBM2 as opposed to just Samsung, so as Raven Ridge isn't here, it's still possible. In fact, it could even be Raven Ridge is delayed to allow for increased HBM shipments.
This is all talk however, it'll be interesting to see how crippled Vega is by low memory bandwidth, and whether it can surmount those to at least be reasonable; and safer to assume it won't have HBM.