Dr. Mario is just Mario in a lab coat, yet he's been decloned from Mario over the years. Paper Mario is not just Mario. According to Mario & Luigi: Paper Jam, he is his own character in a separate universe from the original Mario's. We have three Links and three Samuses in the roster. I think having three Marios would be fine. Do I think he's likely for DLC? No. But saying that Paper Mario is just another Mario is kind of being disingenuous.
I know, if you notice, I said I'd love to have Paper Mario in the game as his own character (especially if Vivian was included in the moveset..maybe a Down Special to use as an attack evade..though I'd accept Bow for that role either) I do admit though that I'd be afraid of Miyamoto demanding he only reference Sticker Star and Color Splash, which is not what I'd want from the character at all, which is why I'm more neutral on his inclusion.
I wasn't referring to his moveset or saying that as a reason not to include Paper Mario, I was simply saying that, as far as Paper Mario as a series is concerned, Paper Mario IS Mario, they don't refer to him as Paper Mario or anything, so Paper Mario is sort of represented by Mario akin to how Mr. L worked as an alt in Project M for Luigi because Paper Luigi essentially IS Luigi, just 2D instead of 3D. This is also referenced in how Peach uses a Pink Parasol in a similar design to the one used by Paper Peach in Super Paper Mario rather then Parry from Super Princess Peach or the green parasol she used as a weapon and in a way similar to how its used in the aforementioned games and Smash during a cutscene in Super Mario RPG.
Also, as I said, discussing the Mario Canon is a Fools' Errand since the worlds of the various Mario series all kind of seem like they don't fit together, such as the various settings and characters featured in the mainline series, Super Mario RPG, Paper Mario, and Mario & Luigi all seeming very different from one another. Paper Mario just features the biggest artstyle shift for the characters, making it more distinct, followed by the slight art style shift used in Mario & Luigi, while the others all feature the same or similar art styles to one another, making them more believable as being in the same continuity.
But even disregarding canon, they're clearly entirely different; in settings, characters, gameplay, basically everything. But I get what you're saying.
Poochy would be hype imo
I wouldn't say entirely different, they all share the same basic settings and locations, such as Paper Mario's version of Princess Peach's castle having a more similar design to Super Mario 64's then, say, Super Mario RPG....though lets be real, every version of Princess Peach's Castle seems to have slight differences from the Super Mario 64 version, aside from the Super Mario RPG one that predates it and has a very different design (which I'm biased towards since I adore Super Mario RPG).
I do think that Paper Mario, from a Gameplay Standpoint, would be a very fun and creative character, especially if he's more based on Paper Mario and The Thousand Year Door rather then the latter three games..which I'm very afraid they'd pull from only if Miyamoto demanded it..which, honestly, might be why Sakurai hasn't included Paper Mario..I could see him dropping the character if Miyamoto demanded he be based on Sticker Star and Color Splash akin to how he said he'd have dropped Pac-Man had Namco insisted on the Ghostly Adventures design.
He probably would, but I don't know how much moveset potential he'd have. I know Sakurai can make a moveset for anyone, but I just don't know how many people are clamoring for Poochy (yes, I know, no one was clamoring for Piranha Plant either lol).