>>35226386>>35226402>>35226407Go back and read the gameinformer interviews
Masuda talks about development cycles in one of them and mentions how it always takes them -at least- 3 years to develop a new pokemon gen, and mentioned that development of the next gen starts at the beginning of the current gen
By that logic, switch development did not begin while SM were still in development, and given that Ohmori took over as mainline director, I highly doubt they delegated switch development to their B team.
It's probable switch development started in 2016 based on the statements above, also given that Masuda told people that it's difficult to make, it seems unlikely that it'd take 2 years of development only (that is unless of course they somehow got the means to speed up development but I'm not sure how, when they don't really hire additional staff due to a "too many cooks in the kitchen" mentality)