As of December 30, 2018, Famitsu digital estimates for Super Smash Bros. Ultimate are at a whopping 309,229 downloads in Japan. Other numbers include 78,756 for Futari de!Nyanko Daisensou (The Battle Cats), 45,387 for Super Mario Party, 33,506 for Dragon Quest Builders 2: Hakaishin Shidoo to Karappo no Shima, 29,219 for Mario Kart 8 Deluxe, and 23,611 for Splatoon 2. Super Smash Bros. Ultimate is available now for Nintendo Switch.
Source: Japanese Nintendo