While I wouldn't say they're frontrunners per se, there's definite rumors swirling around the 16th for two characters, Arle Nadja (Puyo Puyo) and Dante (Devil May Cry). Puyo Puyo Tsu, pretty much the biggest non-Tetris puzzle game out there, is coming to the eShop on the 16th which is a release that was accidentally leaked via early news update and then removed the day of the Pokemon Direct. combine that with the director of the series RTing the Direct and you have some circumstantial evidence. It's also worth noting that Arle was a solid Japanese request during the Sm4sh ballot and the producer of the series has compared Puyo Puyo Tsu and Puyo Puyo Champions to Melee and Ultimate, respectively. Add the fact that much like SNK's arcade games, Puyo Puyo Tetris was a surprising early Switch hit and Puyo Puyo Tsu was ported in its original state to SNES Switch Online and you have an interesting push for Puyo Puyo in the West.
For Dante, we've been told by their social media team to look out for info about DMC3 on the 16th. He's a huge name, and the series producer said that if fans wanted Dante in Smash, they should ask for him on Switch first. Now we have DMC1 and 2 and soon 3 on Switch, with 3 getting special Switch-only features. Hideki Kamiya has also RTed the Smash direct post (again, this could mean nothing) and has joked with Sakurai in the past about a Viewtiful Joe Mii costume getting in. Kamiya is also currently RTing posts asking for Viewtiful Joe in Smash. Now, he's a bit of a troll, but that could mean something.
Right now, though, no one truly knows anything. So it's pretty damn exciting.