Atm it's going to be interesting to see what side order actually unlocks, given that a big pull of OE was being able to play as an octoling afterwards. I also think it's pretty safe to say that Side Order is going to be a roguelike, but what that means in terms of replayability remains to be seen.
I really enjoy replaying parts of the base story mode for Splatoon 3, but there isn't much reason for me to do so in terms of the "grind" (ability chunks, money, tableturf cards etc) so if I can only play for so long in a day there isn't much of a pull. The idea of random-ish level selection mixed with the colour chip and palette system (and we know for certain that there's more than 1 palette) is going to definitely breathe a lot of life into the mode, but I hope there's a reason to replay the mode in terms of chasing rewards that are applicable to the rest of the game, even if it's much less "efficient" than grinding turf or ranked.