The tournament doesn't nessessarily rule it out, I mean there can be a 4 player vs mode not involving the orbs, until the game itself is said to not have 4 player, its better to wait unless stated otherwise. Other games have done this several times, I mean in Halo Reach, they had a mode called firefight in which you fight increasing waves of harder enemies, this mode allowed for 4 people, yet there were submodes like defending generators or firefight versus in which it became 2 spartans vs 2 player controlled elites with the rest of the enemies as allies, as cool as this mode was, it didnt allow for more than 4 players total, if it had then it would have been a much greater mode but sadly it didnt.
Aside from that, I am happy to see an original story for once, I mean generally the only naruto games I did get stuck to the main story and those with original stories generally arn't that good. Because UNS3 went to an alternate ending of the kages managing to fight off madara and Obito retreats with the 7 tailed beasts, this one could just be part of that alternate after war scenario in the UNS3 universe, its not canon but like the many marvel universes created over the years, I don't see anything wrong with an alternate timeline in which they successfully averted the ten tails revival, even if its funny to see the edo tensei just mingling in the crowd. Kinda reminds me of that short from an early naruto movie in which many villians and even minato are present around the stadium while naruto tries to find time to go to the restroom.