I have nothing against Dante, I freakin' love that guy. I think I read they wanted to bring some freshness into the series for this new console generation (Well, it's not new anymore, but...) So they went with a new protagonist and some new gameplay mechanics. I wouldnt mind at all if Dante starred in another 10 DMC's. But to me, it seemed like they were setting up Nero to take over the Devil Hunter mantle, what with him being young/green and Dante seeming much older.
With MGS2, Kojima did the exact same thing. New generation of systems means new main protagonist and new story arc. However, fans hated Raiden, not because he was weak or didnt fit in the universe, they hated him simply because he wasnt Snake. It's the same thing with DMC4; I'm sure most fans that disliked Nero, do so because of their fan-love of Dante and their unwillingness to let a new protagonist take the stage. Knowing that, you'll probably get your wish. After all, Snake came back, even though he was grey haired and coughing up lungs, the fans got their hero back.
How about a comprimise? There's no reason Dante and Nero cant co-star in the next game as well. Actually, me and another DMC-lover were brainstorming about how much fun we could have if we could play DMC5 with co-op, as Nero and Dante. Now, that'd be pretty sweet.