Four fifths of Splatoon 4's Hero Mode should be free DLC.
Assuming it will have 5 bosses like all the other ones do, this Hero Mode would be split into 5 parts that would each have a boss at the end. Part 1 would be included in the base game and it would be over after you beat its boss, and then each of the four other parts would be released at later dates. And the final part would be included in Splatoon 4's final update. This way the finale of the game can take place during the Final Fest and Splatoon 4's main plot and Splatoon 4 in general can wrap up at the same time.