Have a big post to why I think Ninja Gaiden, Doom, and Resident Evil are the three most likely DLC franchises:
Ninja Gaiden
- Koei Tecmo already has content in Smash in the form of the Fatal Frame assist trophy.
- Koei Tecmo helped developed multiple titles for Nintendo including Hyrule Warriors, Fire Emblem Warriors and Marvel Ultimate Alliance 3. They also helped with Fire Emblem: Three Houses.
- Ryu Hayabusa is arguably Koei Tecmo's most iconic character.
- Ryu Hayabusa is also one of the most, if not the most iconic ninjas in gaming, only rivaled by Scorpion and Sub-Zero.
- Is arguably the last big 80s gaming franchise not yet in Smash in some form.
- Is one of the most influential franchises in the hack n' slash genre.
Doom
- "Hints" that might mean Doom is coming to Smash (Mick Gordon's secret project, Pete Hines's comments on Smash, his more recent comment on Nintendo fans and DOOM, Nintendo people saying Doom is a like a Nintendo franchise, Bethesda visiting Japan last year (not Tango related)).
- Doomguy/Doom Slayer is arguably Bethesda's most iconic character (even though he's not originally a Bethesda character).
- Both Doom 2016 and the upcoming Doom Eternal are on Switch.
- Represents First Person Shooters, a genre not yet in Smash.
- Is the most influential franchise in that genre.
Resident Evil
- Resident Evil is the biggest Japanese franchise not yet in Smash.
- A bunch of RE games have released or will be released on Switch.
- Nintendo had a big advertising segment for the series during the E3 Direct, similar to the Dragon Quest one in the February Direct.
- Is Capcom's best selling franchise.
- Represents Survival Horror, a genre not yet in Smash.
- Is the most influential franchise in that genre.
All three, of course, been on Nintendo consoles through the generations as well. And the three companies that own them, Bethesda, Capcom, and Koei Tecmo, have been supporting the Switch a good amount.
I really think the three are the most likely choices for the remaining two DLC slots. While I lean on Resident Evil and DOOM, I believe Ninja Gaiden has a good shot of getting in over one of them.