PS4 matching PS3 is realistic. Switch matching 3DS numbers is possible, but an unrealistic goal. If Switch gets to 20 million lifetime in Japan that's an amazing achievement. But it would be really difficult to predict where Switch ends up being all new systems are coming out in 2020. And we don't know when or what the next Switch revision will be.
I'd have to see what the baseline is for the Switch in Japan after its first price drop/revision before I consider 25m as unrealistic.