God, don't make me depressed with my honest answer.
Wario's Shipyard was a bit of a reference of sorts to the first two Wario Land games,Has the Mario Kart series ever had any Wario Land references? I can't think of any, besides Wario's Car in Double Dash. If that's true, then probably none going by the past games.
Wario's Shipyard was a bit of a reference of sorts to the first two Wario Land games,
The pirate theming, the music track having some minor Wario Land influence,
And a cameo of Bull Wario