Well it's finally been revealed. The possible final chapter in the Soul series.
Producer Tago says that the new installment is going to feature many more new characters that last time, but hopefully old fan favorites will have to be cut. So far only one new character has been revealed. Under the name of Paktros. He seems to be a Sword and Shield based character, but will likely stray away from Sophitia and Cassandra. Possibly a tribute to Link's moveset in SCII.
More details here.