Worldwide sales, Xbox and pc sales plus a new market. Switch will get its version so they won't be losing out on portable sales. Plus they'll likely reuse loads of world's assests so the extra cost on this isn't going to waste. 

Yes, a mainline Pokemon that failed the number of others Pokemon big time would be a failure. A spinoff with smaller budget is a different thing.

You explain that MHW isn't handheld, so that it doesn't need to make the same numbers. But your logic is backward. Developing Monster Hunter World was most likely more expensive than any other MonHun before. And probably big time so.

Increased development cost that result in lower sales? Not a good message. 2M in Japan should be the expected minimum, a decline in japanese sales could be OK if increased western sales can balance it out. But this game shouldn't destroy the devoted user base the series built over time in japan. So the decline shouldn't be too big. 2M is total minimum, below that is bad for Capcom and bad for Monster Hunter.

Yeah, I definitely think it'll be possible. 2-3 mil lifetime I think is doable for the system in Japan.

Yeah, but I thought about it, and actually I can't believe it anymore. The series exploded after Tri. So no longer the same metric apply. Also the more I see of MHW, the more I think it was really expensive compared to earlier entries.

I actually believe it will sell more than 2 million in Japan, I expect something like 3 million, which would be OK. But I no longer can see halving the userbase in Japan as a success.

Maybe.

In my opinion could become a 2 million seller in Japan by the end of 2018 (obv adding retail and digital versions)

Around 1.5 - 1.8m ltd I think.

Why not go for the platforms that sell more? Why should Capcom go multiplat if they expect to lower sales with that?

Look at it this way: Think the new Pokemon on Switch will be a big mainline entry and Gamefreak goes all in with really expanded new graphics and open world with a big budget. How would you react if people make a thread here on VGC and say 2 million in Japan would be an excellent success for this new Pokemon.

That's comparable, X/Y had 4.4M in Japan, Sun/Moon 3.74M. Monster Hunter 4 had 3.44M in Japan. So saying 2 million for Pokemon more or less equals saying 1.5 million for MonHun would be a success.

One thing that has to be taken into account. The 3DS monster hunter titles launched at $40, MHW will be a $60 title.

Second, Capcom has stated this is a game that is designed to appeal to western audiences, they want to expand the franchise and gain new fans, launching on yet another Nintendo Handheld would not help to expand the franchise, they'd just be selling to the same people again. The game they designed to accomplish this could not run on the Nintendo Switch.

Rather than continue to make MH titles exclusively for one system, expanding it into a multi-platform franchise makes sense. The next title can be designed with every platform in mind. Switch/PC/PS4/XBO, and take advantage of the fans  they have gained on other systems with MHW.

I think it is possible.