So big question I've been tinkering with lately:
What about MMOs? Obviously not gonna happen anytime soon, but in the future I think it's an interesting prospect if they want to dabble into the PC and computer games. Something like MapleStory, Warcraft, and RuneScape is what I can consider as big contenders.
I guess the same question applies to big MOBAs like League and Dota.
MOBAs are more likely of those two IMHO. They've at least begun to arrive on the Switch, and the LoL / Dota 2 rivalry (and the boatloads of cash being spent on those two games) indirectly affected Smash's competitive scene a lot. it's what lead to Smashers being sponsored by energy drinks and orgs that started out as MOBA teams - giving the pros a lot of exposure. Sure, Sakurai doesn't care about that, but Pro Smashers helped to show off Smash 4 and Ultimate via invitationals. Without the whole process things would've looked at least somewhat different.
While I'm a Dota 2 guy myself, I won't deny that Valve has other options they'll likely prioritize. Gordon Freeman, TF2 Heavy and Chell most likely. Also, while it's popular in China / SEA / Russia, Dota 2's completely obscure in Japan. Yea, Japan's not known as a computer heaven, but Valve's complete lack of marketing doesn't help.
LoL has probably the best chance. Talked about that before, but with Tencent handling the Switch's Chinese release, LoL's better known status in Japan (LoL's still niche in Japan, but it's an advantage over Dota 2) and LoL's worldwide popularity I've begun to count it as a possible surprise pick. As for possible character from that game, I'm leaning towards long-time headliners like Ryze or Ahri.