Theory 1:
Basically what you said Meg - demonic experimentation that goes wrong so they pick the one from the litter who hasn't gone full-out demon to clean up their mess. Re-creating Dante in a sense, but he's not the real Dante, sort of like a "clone" of Dante.
Theory 2:
It's another stereotype badass c0cky devil hunter who decides he wants to up his rep, and through experimenting he gets some of Sparda/Dante/Vergil/Nero's blood into him that gives him the abilities he's got. And because Dante sees himself as the best in the business, this new guy wants that reputation for himself, hence calling himself Dante. And then the real Dante later comes in and kicks his butt for trying to steal his identity - BOOJA! XD
Theory 3:
It's Dante's son. Either his mother named him after his father, or he changed his name later on, since I think that's what Dante did in regards to Sparda's alias Tony Redgrave. And it's all about this kid kicking butt, being cool, winning over his own fanbase, and pleasing all levels of fans with Dante showing up on the scene when he gets captured? I mean the trailer might not have been in chronological format. Maybe he gets caught in the end (I mean how many teens do you know that get CHAINED in a room when they go into rehab? Srsly?) and Dante comes busting through the door (or ceiling, or glass window) to save him? Tarum tarum tarum!
I like my second theory best, though that's just the fangirl in me retaliating at this guy calling himself Dante.