Firstly, there’s this teaser image released prior to the trailer, showing an image of the new protagonist seemingly clawing his way out of some paper. The link shows an artwork comparison between the protagonist here and the antagonist of Persona 4 Arena Ultimax, Sho Minazuki. The facial structure and pose seem basically identical. The true ending of Ultimax also had Sho leaving, his plans foiled and his alter-ego having disappeared, to go off on new adventures and presumably learn the true meaning of friendship. I find it highly likely that Sho Minazuki is the new protagonist, whether he be silent or not, which this trailer supports.