AMD gave LinusTechTips the right to publish an exclusive video that showcases a VEGA video card prototype. Some parts of the card were covered with tape, so it's impossible to say whether it requires a single 8-pin PCIe power connector or 8-pin plus 6-pin.
That weird little board screwed to the VEGA card is used for debugging purposes as this is a pre-production card. The VEGA prototype uses a dual-slot cooling solution and seems to have a length of about 260mm. This may or may not be indicative of the final product.
The video also contains some more footage of Vega running Doom.