Did the April Update to Mario Kart 8 Add New Characters?

A new update to Mario Kart 8 apparently adds six new playable characters, one of which is brand new to the series. The supposed characters are not available from the start, but if Miiverse user SuperZambezi is to be believed, the hidden six characters can be unlocked by placing first in the 200cc cups. The six characters include:

Dry Bones
Professor E. Gadd (newcomer!)
Diddy Kong
Birdo
Petey Piranha
King Boo

The latest update for Mario Kart 8 went live this morning on April 1.