This would end the series and let Crapcom focus on the reboot.
So it actually turns out that inside Nero's arm theres a part of Mundus ( Dante didnt fully kill him). As time passes Mundus gets deeper into Nero's mind and manages finally to control him. Then he seeks for Sparda. With that sword he could return to his full form with even greater power. He manages through Nero to trap Trish and get Sparda from her ( he either kills her or keep her as a slave). After gaining his full form he attempts to unleash hell, transferring the demon world to earth. Dante realizes he cant stop all this alone. He goes through the portal that Mundus created and goes into the demon world to find Vergil. Dante convinces Vergil to fight by his side. Vergil also reveals that all this time in the demon world he was tortured by Mundus's son. They return to earth, the fight starts and blah blah blah they reach the final battle which will be a 2v2 one. During the fight Both brothers realize that its a few minutes till hell gets transfered into earth. Dante goes through to close the portal and suck all demons with it and Vergil stays behind to make time for Dante. Dante manages to close the portal but Vergil dies (Drama scenes following etc).
What do you think? --- "Might controls everything"
You know what? the conspiracy theory or the idea of freedom and controlling people can be implied indirectly with DMC's timeline and characters, it can also be some system related to the demon world exclusively or demons and humans cooperatively controlling people and demons. Or simply make more plot twist and intelligent kind of story alongside the symbols and emotions that the characters in DMC presented. DMC3 had a good story , style of storytelling, plot, characters...etc i would like to see itsuno improve and build on that style.