That's not really mutually exclusive. Mario Kart infinite could still be a service and be the only pure Mario Kart game for Switch. While there's a Diddy Kong Racing or Smash Racing or whatever later with characters from multiple IPs, different vehicles etc.
Nintendo really needs to embrace the games as service approach for thinks like MK, Splatoon, Smash etc. though. That's the future of MP series, and there's tons of money to be made as you can sell the base game for years, and keep getting money from the base for cosmetic items, expansions etc.