To go out on a limb and speculate a bit here: might AMD be copying the Nvidia playbook even more than we're seeing here? How? I'll get to that in a minute, but here's my reasoning:
Previously, AMD/ATI has been a "gaming first, everything else second, third, or whatever really, we don't care, how about some games?" type of company. Before the Radeon Pro push, the FirePro line saw little adoption compared to Quadro cards, despite being far cheaper. Nvidia has since the Kepler days been pushing "pro-ish" cards (Titans) first on new architectures, and recently relegated the truly pro-level cards to dedicated silicon - due to the use/need for DP compute and the like, which takes up silicon area with no gains for most users.
Now, we see something similar from AMD: A Radeon Pro card being the first from a new architecture, with a somewhat inexplicably large die size (despite having 2x the SPs of an RX470, the die is significantly larger than 2x the 480/470 die - and that's without accounting for the die area savings due to HBM vs. GDDR5). AFAIK, the DP compute rate of Vega hasn't been disclosed, but I'd gather the extra hardware required for packed math does represent at least some of the die size increase, and it would be logical for a pro-level card to target something better than 1:32 DP compute rate - which would explain even more of the large die.
There used to be rumors of two Vega dice, yet in recent months, all we've been hearing of is the one presented to us yesterday in the Vega FE. Would it be entirely crazy to think the other Vega die might be a consumer-focused die, ditching packed math and whatever increased DP compute rate the VFE has, and using the freed-up die space and increased power efficiency to put in more CUs? After all, packed math has near zero value in the consumer space, as does DP compute. If they could push power efficiency to a point where we could have a 5-6000 SP Vega gaming card at tolerable power consumption at <600mm2, that would trounce anything Nvidia has to offer, at least if they can push it to 1500MHz or thereabouts. It would also make sense to launch it later, as a consumer focused "response" to Volta, while in the meantime selling partially disabled Vega ... 10? whatever the VFE has cores as a lower-end (and still reasonably competitive) stopgap until then. After all, it looks like even the VFE is reasonably competitive for gaming.
Of course, again, this is entirely unfounded speculation. But some times, dreaming is fun.