I'm in support of them. I made my explanations clear in the Rate Their Chances today, but I'll put them up here again. I hope you don't mind.
Inkling as Assist Trophy: Want: 100%. While I know this is unusually high to give a character that's so recent a place as an Assist Trophy, I believe it would be a great way to introduce people who are both familiar or unfamiliar with Nintendo's newest IP. Basically, it'll be a bit like Roy from Melee, who was included in Super Smash Bros Melee alongside Marth to represent Fire Emblem; giving people a taste of what Fire Emblem is like. Roy was included to promote Fire Emblem: Fūin no Tsurugi, (FE6) and it was a clever move by Sakurai. If it worked for Fire Emblem, surely including the Inkling as an Assist Trophy would benefit the upcoming Splatoon game, by showing off the main characters in Smash Bros as an Assist Trophy.
Chance: 20% However, Splatoon has only just come out of Nintendo's delivery room of IPs, and really brought to the attention of gamers since E3 2014. Whether or not Sakurai has seen the development of Splatoon, I don't know. Perhaps it's a bit too recent to be thinking about them in Smash Bros. Not to mention, there's been no sign of them having any involvement so far, so it's a little uncertain.
Inkling as playable character: Want: 40%. While this is significantly lower than my Assist Trophy hypothesis, I'd be happy if they made the Inkling as a playable character. Like I said, she'll be representing her future game like Roy , and that would be a good choice. I believe most of what the Inkling can do in her upcoming future game can be translated into Smash, so here's my move set for Inkling:
She's predominantly a projectile and camping based character, relying on her paint weapons to slip up her opponents on the ground, but she is a weak fighter up close, relying on her projectiles like the Mii Gunner.
Move-set
Neutral Special: Paint Shot: The Inkling prepares her paint gun and charges up a projectile made of paint. The longer you charge up the attack, the more damage it does. While it's being charged, the Inkling can aim her paint gun up or down for different effects, with the upwards version being an effective anti-air weapon, while aiming downward causes more paint to splatter on the ground in front of her, which makes it easier for her enemies to slip and follow up with combos when they are down.
or Side Special: Squid Rush: The Inkling quickly morphs into her squid form and dashes along the ground, spreading a trail of paint in her wake. It has short range, but it can be used to get around foes quickly and deals minor damage to them. It's very quick, and allows for a brief escape from enemy attacks.
Up Special: Paint Rocket: The Inkling shoots pressurised paint from her paint gun, shooting her upwards like a rocket. It has very little horizontal recovery, but it allows the Inkling to quickly gain altitude.
Down Special: Dissolve: This move can only be done on a paint splatter she made - Inkling quickly dives into the ground, able to avoid damage for a brief period of time, however, she can only move around in the space that she has coated in paint, so she can't move very far if she hasn't coated much of the ground in paint.
Final Smash: Paint Barrage: The Inkling takes out a massive paint bazooka and fires giant globs of paint around the stage, able to coat more of the stage in paint than her Neutral Special. It deals a lot of damage, but can easily be avoided.
Chance: 10%. The challenge here is how recent she is, and if Sakurai is aware of Splatoon. He may or may not want to represent it, but given it's such a recent concept and won't be released until 2015, I'm guessing it may be too late to add them in now. Those are my doubts about Inkling as a playable character.
These are my views on the Inkling for Super Smash Bros for Nintendo 3DS and Wii U. If she doesn't make it this time, and if Splatoon eventually becomes a successful product for Nintendo that they are willing to continue, I'd say that Inkling has a good chance of appearing in Super Smash Bros in some way. It may not be in these games, but I'm in full support for Inkling.