I feel like an ARMS 2 will probably happen, because while ARMS didn't set the world on fire like Splatoon did, it still did pretty well for itself at 2.72 million units, so I feel like they'd give it at least one more go. I don't think it would get another character or anything, but I feel like Min Min would stick around. Plus outside of the Ice Climbers in 4--something that only happened due to technical limitations, mind--we've never completely lost a first-party series in terms of playable characters. First time for everything and all that with the potential cuts on our doorstep, but I feel like that might help Min Min a little at least.
Byleth, Pyra/Mythra, and Min Min being the only Switch characters might also be benefitted by the Switch being such a huge success and higher-ups wanting to ride that momentum so to speak, since next Smash is the game that'll presumably have the Switch's whole 7-8 years to take into account. Not an end-all be-all obviously since the DS still hasn't been topped by the Switch yet and we only have one DS character, Lucario, but may be something to take into account.