I think we can all agree here that handheld gaming devices are super popular in Japan and if my statement does come true I hardly think it will be a shock to anyone. But more important Is what effect will this cause. Will it mean the Switch will get a lot more 3rd party support from Japanese developers than the Wii U as well as even exclusives like Monster Hunter (which wouldn't exactly be a shocker either considering the 3DS). What else will it cause? Contribute to overall higher sales than the Wii U globally? (Especially considering Japan accounts for 22.40 million of the 3DS's sales) Just something interesting to think about what effect the Switch's Japanese sales could effect the system overall not just in Japan but on a global basis.

EDIT: Just thought I would include this as it's pretty relevant to the topic:

PS4's Japan sales number's: 4.34 million.

3DS's Japan sales number's: 22.40 million.

Wii U's Japan sales number's: 3.32 million.

(Stats used are from VGChartz sales numbers updated as of 18th of Febuary 2017)

The bad thing is that games might only be released in Japan if the Switch only does well there.

Almost definitely, but I don't really think that's a huge accomplishment considering the climate there.

Won't have any effect on PS4

Easily

I would worry about that too, but Nintendo lately has taken a real shine to localising a lot of games that where or would have been Japan only. On the upside region free is always something to fall back on.

Well hopefully Japan will flock to it, but 3ds has been selling rather well lately so maybe there's hope yet for switch

Well if the games are simple platformers, then fair enough.

I'd say it is almost a certainty in Japan. Once 3DS stops and support shifts all to Switch it could be by significant margins as well.

VERY easily. Japan heavily favors portables over consoles. Vita is doing well in Japan but now that is dead thanks to Switch.