The next game has gotta go through 5 years since the demons started to emerge.
Dante rebuilds his old home with Kat's help, coming up with good ideas for the new home base. Plus trying to find a good name.
Kat's father has GOT to be Arkham. Arkham serves under Nelo Angelo who is Vergil wearing a new mask to hide his face.
Trish can return as something new. But we know she's adapted from Beatrice from Dante's Inferno.
Angels show themselves. At first they see Dante as a threat and so as Vergil, but later he proves himself to them that he can protect humans like Eva and the others do. Phineas returns and also gets help from an angel who was an old friend of Eva's.
In DmC3, I wanna see Nero show up as a cambion. Remember Blade II, Nero can be some child experiment used by rogue humans secretly trying to create their own nephilim based on Dante's & Vergil's blood.
In DmC4, Sparda's story is revealed
DmC5, Dante & Sparda are reunited and fight together.