The only thing you get after the credits is an achievement. And no, there is no hidden ending in Limbo. If you beat the game without dying once you'll get another secret egg (and is required to get 111% in the game, but there's no achievement for that), but otherwise there's no secret ending.

The "Limbo of the Patriarchs" or "Limbo of the Fathers" (Latin limbus patrum) is seen as the temporary state of those who, despite the sins they may have committed, died in the friendship of God but could not enter Heaven until redemption by Jesus Christ made it possible.