If this card is going to arrive soon it seems AMD has done a splendid job of keeping the card secret until the very last moment as no one seems to have an idea of what it is. Whether the "687F:C1" is really a Radeon RX 490 is unknown, but due to the way Ashes of the Singularity recognizes the card, VideoCardz believes it's a single-GPU card.
Coupled with the fact that this mystery card delivers performance comparable to a GeForce GTX 1080, this is a strong indicator that it's indeed a new model based on the Vega10 architecture. Guess we'll have to wait a bit longer to find out what this is all about.
Personally, I don't think it makes sense to launch Vega under the RX 400 series, and the launch doesn't seem imminent because AMD reiterated last week that Vega is on track for a "first half of 2017" launch.