Paper Mario's chances at being in FP2...
Pros: Super Mario Bros. 35th anniversary, which may give us a trilogy of the first three games, or remasters or simply re-releases. This in turn could make Paper Mario get in Smash. If no such games, then simply ending the fighter's pass 2 with Paper Mario since the anniversary will be concluded.
Cons: Origami King release would be a great time to release Paper Mario but it didn't happen. Origami King spirit event could also be a disconfirmation, as if Paper Mario were in the fighter's pass then they would save them 'til Paper Mario got released as DLC spirits.
Tinfoil hat: When introducing a new character, Sakurai feels it is important to focus on the character's roots. But since the Paper Mario franchise has greatly strayed away from its roots (and Nintendo/Miyamoto kinda "hates" those games...), Nintendo/Miyamoto would want Sakurai to focus on the later games, which Sakurai can't do since it's against his philosophy like the cultured man he is. So they basically said to him: "either our wish or no Paper Mario" and Sakurai has said no to that since Smash 4...
My take: Honestly the only ray of hope I have left for Paper Mario joining Smash is if Nintendo has plans to release one (or more) of the first three Paper Mario games in any shapes or forms. (This would also mean that we would get more spirits from those games, debunking the Origami King spirit event "disconfirmation".) But my string of hope is that they could simply be saving him for last to conclude the Super Mario Bros. 35th anniversary. Either one of those two scenarios seem plausible but this is only wishful thinking at best. (I personally don't think he will be a character but it ain't over until it is over if y'all know what I'm sayin'...)