Looks like five more racers are coming to Mario Kart 8 Deluxe at some point.
5 Characters Who Could Be Next in Mario Kart 8 Deluxe DLC
Mario Kart 8 Deluxe is getting 5 more characters
Mario Kart 8 Deluxe Getting Five More Characters in Future DLC Waves - IGN
A Look At The Mario Kart 8 Deluxe Character Select Screen - My Nintendo News
Mario Kart 8 Deluxe update adds 5 more extra character slots beyond Birdo
Mario Kart 8 Wave 4 update leaves 5 more spots for characters : r/mariokart
Mario Kart 8 Gets More Characters Because It'll Never Die
Mario Kart 8 Deluxe Booster Course Pass Wave 5 Thoughts - KeenGamer
Mario Kart 8 Deluxe' Booster Course Pass: Buy or Bye? - GeekMom
Mario Kart 8 DLC hints at more returning characters after Birdo reveal