I'm checking around and see if Octoling truly have a chance but it seems that they could have their shot getting in Smash Bros if they are interested enough to get them into.
It could be a similar situation with Melee's Ganondorf.
July 5th, 1999: The project proposal/initial design document for Melee is completed.
August 2000: They finally shown a tech demo of upcoming Legend of Zelda game with Link and Ganondorf battling it out.
Melee's Ganondorf is definitely based on Tech Demo's Ganondorf
Information on Ganondorf's situation
Ganondorf was a special case and was described by Sakurai to be an ‘extremely lucky character’ to have been included in the game. His model was originally made for the SpaceWorld 2000 tech demo and happened to work well with Captain Falcon’s animations thanks to their similar body shapes.
Also Sakurai's comment:
A fan e-mailed Sakurai about the possibility of making King Dedede a clone of Kirby in Melee, to which Sakurai responded: “Dedede as a Kirby clone? I…can’t do that! That’s impossible! When deciding clone characters, the body structure has to be exactly the same.
Octolings and Inkling shared the same body structure, and their heights are similar so it shouldn't be any problem. I honestly think there is only one thing that might held them back from becoming an echo fighter is how complex their movesets were. That's probably same reason why Alph didn't become a clone in first place (I know it could be 3DS limitation at play but still)