Being that these games would most likely be released in Japan first, the only other platform that makes sense is the PS4, which hasn't sold very well over there. I was thinking M2 would continue to focus on a Nintendo system and given that the 3DS / New 3DS don't have the hardware performance to run Model 3 games, Switch would be a perfect fit.
I also think that if it does happen, a Model 3 Classics series would't get announced until the Switch has been on the market for awhile. The 3DS launched in Japan February 2011 and the first Sega 3D Classic (Space Harrier) was released there December 2012.
So being realistic, if Sega & M2 went ahead with bringing Model 3 games to Switch it might only happen in late 2018, but if PS4 was the target platform it could happen much sooner.