Paper Mario
Chance - 45%
Quite possibly the most popular Mario subseries after Mario Kart. Though it is still Mario, the Paper Mario series is a completely different universe with its own self-contained lore, similar to the Donkey Kong Country series. PM, like SMRPG before it, represents a kind of platformer-RPG hybrid that helped make RPGs so accessible and user-friendly to the masses, at least from my perspective and experience. If Hal and Namco are looking for an additional Mario series character, the paper-thin hero is among the front of the pack in terms of significance and unique quirks.
The low-ish score is primarily due to the lack of PM material in Brawl, after the megaton hit TTYD critically was, with SPM trailing not far behind. If those two games weren't enough to warrant a spot for PM then, I dunno if Sticker Star was enough to get him in now, despite the financial success it was. The stage today shows that "Hey, we're flirting with the idea.", but it's not an ironclad confirmation.
Want - 95%
I do have bias for this little guy though. He was my second-most wanted newcomer after Robin. Badges, Stylish Moves, Paper Abilities, Partners, Pixls, Stickers, Paperification, the guy's had something new thrown into his repertoire with each installment and he's used them well. PM wouldn't have to take material from just one game, he'd be able to take material from all of them equally and go nuts everywhere, including the stage that seems to follow in his footsteps and take a little from everything as well. Jack-of-all-trades, master of them all as well.