From a post by 'Wotc_Eric' (aka Eric Sorensen) on the Wizards Community page:

[easybox]Hey guys - I just wanted to let you know I’ll be at PT San Diego this weekend. If you’re there, be sure to check out Champion Challenge where we have special guest stars (seriously, they are real celebrities, come by to see who it is!) dueling with the upcoming Duel Decks Phyrexia vs. the Coalition as a preview. Here’s a sneak peek for you folks on Wizards Community: the alt art mythics are Phyrexian Negator and Urza’s Rage.[/easybox]

[easybox]Some of you might be surprised to see Phyrexian Negator. It is true that while we’ve been able to make premium versions of cards on the reserved list, we’ve so far only used them for promotional purposes (Negator was a judge promo, for example). We’ve taken a look at our special products and feel that we can create a better game experience for you by taking this step. How cool would it have been if Sliver Queen was in the Premium Deck Series?? Don’t worry that we’ve lost our minds. When From the Vault: Relics comes out, you won’t see these cards: [Shows pics of Black Lotus and Moxes]

But you will see this![/easybox]

Thanks to @mtgcolorpie for the tip!