I really don't want him, but there is a lot of stuff pointing towards it being Dante from Dmc. Both the tweet from the Dmc Twitter account, and the fact that Dantes voice actor has been hinting towards being involved with Smash.
I hope all of this is wrong, and that we actually get a Nintendo character THAT IS NOT A FIRE EMBLEM REP included. (I'm also secretly hoping it's Master Chief)
After Phil Spencer and Microsoft were willing to play ball and let my "Most Wanted Newcomer" Banjo-Kazooie join Super Smash Bros Ultimate, I have a newfound respect for them am forever grateful and I would love to see Nintendo return the favor by letting Master Chief join Smash as it would show how strong and great their business partnership really is.
Master Chief getting in and would be internet breaking and jaw dropping hype to see him fight Mario as he is one of gaming's biggest icons and the face of the Xbox brand, He's got everything from moveset to status to make for a big and great character reveal.
I personally don't have a lot of history with the Halo franchise since I grew up mainly with Nintendo consoles, But always thought it was a pretty cool series, Not to mention you got all those rumors of Halo Master Chief Collection coming to Switch.