Codemonkey76 points out that the listing is now on the US Xbox.com page right here. Interesting!
So, at this point, one has to wonder if we're looking at a guerrilla marketing campaign. Not only have achievements popped up for Mass Effect DLC "Pinnacle Station," not only has the Swiss Xbox.com priced the thing, but now a Pinnacle Station theme has actually shown up on Xbox Live. ... Oh, didn't we mention? It's still unannounced.
While you wait for someone to actually confirm its existence, check out the gallery below and see if you're able to extrapolate any hints about the content from the images we captured.