I understand people's skepticism, I didn't believe that octolings were going to be available in splatoon 1 and I was less dissappointed than most, but this time around I do feel there are 3 reason that this will most likely come about
1. Marina, the octoling co star, of off the hook to me shows that most liekly will be playable octolings in spaltoon 2, why, well most of the animations are there we see in the single player campaign, plus this is the first time we are seeing facial expressions and gestures which we never saw in the first game which would be necessary in order for us to be able to have in order to switch gear.
2. There is code in the game for both an octoling female and a male in the original code there was a icon for octoling but there only the female in the original code, this time around however there is a male icon in the code giving me hope that this might happens
3. Lastly, the splatfest in the last splatfest of splatoon 1 we had Callie vs Marie (which kinda went south) but the idea of a marina vs pearl can not have an octolings vs inklings along with it in the final battle, so all things considered, that plus the huge desire of the community I think it is likely that we will see them in Splatoon this time around