Shot in the dark, I think they're gonna add a Devilman story mode.
I've been trying to figure out why they're being so weird about Devilman. He's been teased twice now but they still don't count him as officially revealed. I like Devilman but it's not like he's a mega blockbuster character to deserve all this build up.
With regards to the Sparking/Tenkiachi series though, he's kind of a big deal. He has a super unique ultimate attack that does more damage the more evil the target is. That alone already makes him stand out. But his what if scenario in BT3 is probably the most discussed and popular to come from that game.
So that got me thinking. What Ifs were a big selling point of the story mode, and even characters who you wouldn't think would offer much got their own story paths (see Goku Black and Jiren). Devilman is the perfect choice for a sort of joke story path. Just him appearing out of nowhere to take on the villains. That little tease of him staring down Goku Black on the ruined future map feels like it could be ripped straight from a story battle.
Probably not gonna happen, but I could see that being a fun little "one more bonus" thrown in during the next trailer for the Neo expansion.