In the last update that they rolled out in Japan, it added cross-site play. Since the game was released in Japan about a year before the International (US/Europe) versions were, they have been ahead of that curve slightly and today it was announced that they have the latest updates in hand ( click here for news on last year’s update for the US)
It was originally mentioned that Bandai Namco’s Mario Kart Arcade GP DX was an online game and as a part of that, annual content updates would be sent to the machines.