Doesn't really matter, handheld are much more popular in Japan than home consoles (just compare 3DS numbers and PS4 numbers, 3DS sold 5x better than PS4 in Japan), and Switch is handheld console also, and it will have one most popular IPs in Japan, lotsa 3DS owners will do upgrade to Switch in any case, even some Vita owners.
The 3Ds is the 3DS. As of this moment, it doesn't look like the switch is going to have the sort of library or pull of the 3DS. Every developer that wanted to go mobile had no choice but to opt for the 3DS. Now the situation is an intensely competitive mobile market and a drought of 3rd part developer interest.
And Switch is Switch, console thats a handheld also, on Japanese market, and it will have most popular Japanese IP that is Pokemon and other very popular IPs like Monster Hunter, Animal Crossing, Splatoon, Yokai Watch...on other hand PS4 is not selling great on Japanese market. Its not relly hard to understand that Switch will easily outsell PS4 in Japan (PS4 even had problems to outsell Wii U on Japanese market), not only that handhelds are much more popular than home consoles in Japan, but Switch will have very strong and popular IPs in Japan that PS4 want have.
It just will not happen, the PS4 has so much better JRPG and Japanese game support, it is impossible for the Switch to outsell it. PS4 will also have the best version of Dragon Quest XI, so no. Also the Switch is just too large for a mobile device.
So it's impossible that console thats in same time handheld, that will have Pokemon, Animal Crossing, Monster Hunter, Splatoon...to outsell PS4 (home console) on Japanese market!? Ok than. :D