I'm going to have to agree with BluePikmin, that kind of stuff is said (and is true) for lots of new IPs, but it doesn't mean they can automatically stack up to series like AC, Wii Fit, Xenoblade, Punch-Out, etc. or any of the other series that already have been included, so really the only way we'd get Inkling imo is if Nintendo insisted on it for promotional purposes, and them pressuring Sakurai over the roster to that extent seems unlikely since he's usually given pretty free reign (at least by them).Well I mean, the possibilities of the moveset are just too good to pass up in my opinion. Inklings seem like a pretty popular choice when it comes to DLC anyway, so there is little downside to adding this character imo.
And honestly I don't see them being that popular, probably due to most people not really expecting them. Like it always does their popularity will probably spike closer to release of the game, but at that point I doubt Sakurai will still be in the stage of accepting characters for DLC, they'll likely have been decided already. They're probably already decided now. I don't doubt they'll be a definite contender next time around, especially if we get multiple Splatoon games by then, but as for this time... I think they arrived too late to the party.