Any other companies I might have forgotten that have a chance, or are we still sticking to our core 7 (plus any companies that might have already been in the pass)?
I do have two wildcard companies. Note, wildcards. I bring them up because if they do have upcoming projects on the Switch, then they've suddenly entered the race:
Riot Games (Tencent): Yes, I've talked about them. A lot. But Tencent's collab with Nintendo doesn't stop at bringing the Switch to China.
They actually got the okay from Nintendo to make a Pokemon game themselves. Also, Smash in China is an almost no-brainer at this point (I'd say Late March / Early April 2020 at the earliest). And with one Chinese favorite already in (Terry) I bet they want in too.* They only have one viable option though - Riot Games' League of Legends.
Riot recently announced an
upcoming fighting game (I'd presume featuring LoL characters). But, even if the fighting game devs involved have experience with simple fighters, we have no idea how far along it is or if it will be on the Switch. If the fighting game does arrive, that could be a major "Watch out!" sign.
Valve: Valve has the opposite problem from Tencent - lots of viable choices, almost no presence or signs pointing to Nintendo. I stand by Gordon being the most likely Valve choice. If the Valve-Nintendo talks did happen as rumored then Sakurai and co. wanted him specifically. That said Gordon does need Valve to get something going on the Switch - an Orange Box port is the safest bet. For him, Heavy and Chell. I'm saying this considering how Valve is run nowadays.
One game could upend it all though: the Dota 2 spinoff Dota Underlords.
The one with the next level crossplay. Underlords' head of development did also state this: while the PC and mobile versions take priority
other options are a possibility. Once Underlords is out of beta and released (it's been in a rapid beta since late June). The Switch could fit this game really well.
I know, neither MOBAs have a real presence in Japan. But Sakurai is someone who looks far and wide. Wouldn't be surprised if he has heard of the genre - especially if he's met people from either company. If there's one "What the?" third party pick, a MOBA pick would be it.
*(Sidenote, Nquoid - Tencent's activities range from fair to really, really scummy. If Nintendo entrusts a Pokemon game with them I don't think they'll have much of a problem with Activision.)