Lycanroc
Chance: 75%
It's like having a death wish to say this on Smashboards, but I'm saying it anyways.
I think Lycanroc has a better chance of getting added than Decidueye.
Now before you start bashing me for saying such ludicrous things, hear me out. Every Pokémon rep we've ever had on the roster has had a notable role in both the games and, more specifically, the anime. It seems like Sakurai takes into account the anime when he makes his decisions regarding which Pokémon will be playable. Why? I have no idea, but whether it's coincidental or intentional, the trend is definitely there.
With that in mind, let's see what Lycanroc has done so far in the anime. Both the original forms debuted in episode 15 of the anime, and in that same episode, Ash caught a Rockruff. Gladion owns a Midnight Lycanroc, and Olivia owns a Midday Lycanroc; Ash's Rockruff developed a rivalry with both. The rivalry is heavy plot point for Rockruff, and it's what ultimately caused it to evolve into the newer Lycanroc form, Dusk Lycanroc. In addition to the anime series, Cross, a character from the 20th Pokémon movie, owned a Midnight Lycanroc.
Now what has Decidueye done? It made its debut in episode 63 of the anime alongside the other final evos, Incineroar and Primarina. However, it only had a minor role as a challenger for Masked Royal and his Incineroar, the real focus of the episode. And...that's it. That's literally all Decidueye has done so far in the anime. And what about Rowlet? Well, even though Ash does own a Rowlet, it's been designated as the "comedic relief" Pokemon while Ash's other Pokemon (namely Torracat and Lycanroc) steal the spotlight and get the real character development. Frankly, seeing Rowlet evolve at any point would be very surprising, and its massive popularity in Japan likely chains it down to permanently staying as its cute first evo.
Nothing against Decidueye and his supporters, because I genuinely do think the guy would be a unique addition. I'm just not seeing the promotion that's usually associated with Pokémon who get in Smash, and that makes me wonder if he's as likely as we say he is. Gen 7 is all but wrapping up now, so unless Game Freak is adamant about continuing to promote Gen 7 Pokemon in Gen 8, the promotion we've gotten so far is basically all of what we're gonna get. Looking at everything that's happened so far, do I think Game Freak and the Pokémon Company as a whole has done enough to prepare us for a possible reveal of Decidueye in Smash? Honestly, not really. If Decidueye was planned to be in Smash, I have a feeling we would've seen a MUCH bigger push in it's promotion. So far, it doesn't really feel like Decidueye has been pushed harder than other popular Gen 7 Pokémon, let alone Incineroar or Primarina. I know people like to bring up Pokken Tournament as an example of Decidueye being pushed, but they forget that Namco was responsible for many of the additions to the roster (Game Freak originally wanted Pokken to be exclusive to fighting types). Hard to say whether or not Decidueye got in because it was pushed by Game Freak or because Namco itself wanted to include it over other Gen 7 Pokémon. Not that it matters much. The Pokken Switch port was revealed in mid 2017. We have no guarantee that Sakurai even knew Decidueye was on the roster when he settled on his list of Smash newcomers.
To sum it all up, I think people are putting all of their eggs in one basket with Decidueye; they're neglecting to look at Pokémon who have gotten a heavier promotion like Lycanroc and Mimikyu. The archer bird is by no means the shoo-in people make it out to be. Based off how much promotion it got, I feel confident in saying Lycanroc has a good chance of being the front-runner for the potential Pokémon rep.
Want: 100%
If the Lycanroc icon in my sig and the lengthy post I just made didn't cue you in...
Mike Jones prediction: 4.4%
Nominations: Mipha x10