Hardware limitations would hardly be an issue, with the Octolings.
And again, with the Smash Bros Ice Climbers, you were talking about content that was under development BEFORE the game's release.
When the game itself was still in development.
It may be a small difference. But it is a difference nontheless.
I concede that unexpected things always happen and Octolings could very well be cancelled.
But DO NOT deny the evidence that has been presented and say "Octolings shouldn't be playable" just for the heck of being a jerk.
(I meant those YouTube comments, not you BTW.)
And currently the evidence speaks a clear language. That we have very high chances of getting playable Octolings.
I'd agree with you there; I would bet on Octolings becoming playable in
Splatoon before
Splatoon 2 comes out (and that's not a matter of if, but when). There is the small chance, however.
Hardware limitations is most likely not an issue, but there are other reasons why something might be canned. The other reasons I stated were if time ran out (no chance of that), budget ran out (this is possible), or there's a glitch they must fix (also possible, particularly with headgear and clipping). Other possibilities, now that I'm thinking about why projects are canceled (this is a hot topic in anime right now with
Rokka of the Six Braves's standard edition being pulled AFTER people had already paid pre-order money into it): There may be an order from higher up to cancel the project for any number of reasons (possible but unlikely), something illegal may have been done during the project that would get the company in trouble (very unlikely with this), an important person on the project leaves (this is always a lingering possibility with anything), or enough time has passed that the project's viability has become unfeasible (not for another few years).
But I think Nintendo knows about the Octolings' popularity and will make every effort, within reason, to make them playable. For people who don't like them, there is always the option of not using them, after all.
Note that, in my third paragraph, the likelihoods are specific to the Octolings, but the reasons themselves are general. Here are some general cases: Production on the Gizmondo was halted due to the Swedish Mafia's involvement in its creation.
Sonic Xtreme was canceled due to a corporate restructuring with the game caught in it (which would fall under "order from higher up to cancel the project").
JoJo's Bizarre Adventure - Stardust Crusaders, while not a canceled project, spent 20 years in development hell because another company bought the rights to adapt
JoJo's Bizarre Adventure and sat on it--
Stardust Crusaders happened because those rights expired.
Pinball Circus was canceled in 1998 because it was discovered to be too expensive to manufacture in large quantities; it was then revived in 2012 but canceled again due to the death of Python Anghelo, its creator, artist, designer, and overseer.