At its E3 Direct, Nintendo dropped a bombshell. A direct sequel to The Legend of Zelda: Breath of the Wild is in development for the Switch. Naturally, hype is off the charts. But prior to this, another Crown jewel of the Switch was also thought to get a sequel, Super Mario Odyssey. The thinking goes that since BotW is getting a sequel, Odyssey should get a sequel too. That logic is really flawed IMO. It makes sense for Breath to get a sequel because most Nintendo systems usually get at least 2 Zelda games to begin with, so naturally a sequel to Breath of the Wild isn't that surprising. Okay.... Well Galaxy got a sequel, ergo, Odyssey should get one too. Here's the thing, Galaxy 2 only happened because the team had more ideas than disc space for the original, and since the Wii didn't have the infrastructure for large scale DLC expansions, a sequel was necessary. If the team actually had more ideas in mind for Odyssey, we would've seen DLC expansions for it by now, but here we are, almost 2 years later, and the most we've gotten was some extra costumes and a Labo VR mode. It's safe to say that much like most 3D Marios before it, Odyssey is a one and done deal.
So yeah, no Odyssey sequel is coming as far as I'm concerned. What I think is more likely however, is a spiritual successor to 3D World. Odyssey was a smash hit, but I feel there's still a market for the more arcade, multiplayer-focused style of 3D Mario game, and thus a game like 3D World, but not necessarily a sequel to that game, is more likely than an Odyssey 2. It'd also be a good fit for the multiplayer focus of the Switch as well.