For as long as the series has existed, Mario Kart has always had three set speed difficulties: 50cc, 100cc and 150cc. I have generally found them to offer a standard challenge across all games, and once you have mastered racing in 150cc, you receive a comparable challenge in each game.
Hoping to offer an extra speed boost and challenge for veterans to the series, Nintendo have today confirmed that a free update to Mario Kart 8 will offer a new 200cc high-speed class for all tracks. This update will be available on April 23rd 2015, the same day that the purchasable Mario Kart 8 DLC Pack 2 arrives on the Nintendo eShop. It is unknown if there are any unlockable goodies for successfully completing this difficulty setting.
You can read my June 2014 review of Mario Kart 8 HERE.