Did you forget? With the exception of PC, they no longer offer season passes before the full season has been released. It doesn't matter what table they start with in order to sell the season.
There was a comment on the Twitch feed about the season pass. I didn't write down the quote but essentially they were rethinking offering the season pass at launch based on the negative feedback they got not having it. So its quite possible there will be a S4 pass offered at the start on other platforms - with the exception of iOS, that being out of their hands.
Even if its just on PC they need a pretty beefy table at launch. Last season they launched with Fish Tales and also announced a few other coveted tables that would appear during the season. They'll want another big announcement for their S4 launch to get people anticipating what's to come. Launching with something like Bone Busters and naming a few other highly anticipated tables to appear later in the season would be pretty disappointing. And I think The Gateway would make for a better table to use as a reveal of what's to come rather than a launch table.
So I'm still thinking they need something big and beefy to launch S4 with and Road Show fits the bill.