AMD is postponing the release of the so much waited Vega cards just because they want to sell and sell the RX series to the maximum and they are doing it perfectly until now. We have to wait until September for the Vega cards which will be more powerful than RX both in mining and gaming.
AMD is widely reported to be having issues with Hynix not having enough HBM2 production to meet the demand for the consumer Vega cards (the PRO Vega Frontier edition has been released and is for sale, on Newegg among other sources, but that's a low-volume card).
This does NOT directly affect the RX series at all, what is probably limiting AMD there is lack of foundry capacity at GF to handle both the unexpected SURGE in demand for the RX 570/580 AND the ongoing demand for Ryzen, the demand for the XBox One X apus, ET CETERA - AND the fact of "lag time" between they can place an order for more chips and when they actually GET them weeks or even months later.
AMD likely also doesn't want to risk over-ordering chips then having to hang on to them (with a lot of CASH tied up by excessive inventory) if the current cryptocoin mining demand drops unexpecedly - and they're probably making a lot more per chip WHILE the demand lasts, while worrying about what it's going to do to their market share WHEN the collapse happens and there are suddenly a ton of "used" cards on the market killing a lot of the demand for new ones.
It is telling that the last "amendment" to the agreement between AMD and GF allows AMD to use OTHER foundries to make stuff, if they pay GF a "penalty" for each wafer made elsewhere. I keep wondering where they're going to find ANY spare capacity to use that part of the agreement, as TSMC is booked out solid as well and Samsung is pretty busy too with their own stuff and the NVidia GTX-1050(ti) making.
While the Vega cards MIGHT be more powerfull for mining, it's unknown at this time if they will be powerfull ENOUGH to justify for mining at whatever price point they end up selling them at.
The Fury wasn't exactly a popular card for mining in it's "new" heyday for that very reason, though at CURRENT pricing it's a pretty good choice.