We don't have access to accurate digital numbers so I'm not going to speculate. It could be anywhere from 100k to 500k.
If Minecraft was released from the start physical... nah not even then. I don't think you appreciate how ridiculous 5M is, or the fact that it has been released on like 5 platforms already.
It would have to have significantly better legs than Splatoon 2 has to this point to make up for any deficit that it would get in that comparison from the first few weeks of sale.
YouTube views feels like a shaky way at best to measure potential sales.
It could also be, well above 500K.
It's far from ridiculous considering how it has historically sold on other platforms which weren't successful in Japan. The fact that it has been released on a lot of platforms which didn't have mainstream appeal won't hurt it's potential on the Switch. While comparing the Switch version of Minecraft to the Mobile version definitely provides certain advantages to the Switch.
It will no doubt have ridiculous legs but it doesn't need to match Splatoon 2 to reach
5M in Japan. Splatoon 2 is on pace to be very close to
3M by it's first anniversary it could very well surpass
5M by the end of 2019. Minecraft out of all the games launched on the Switch so far, will undoubtedly be the second biggest evergreen on the platform behind. It's eShop performance over the course of the last year is testament of this.
YouTube views are used to simply demonstrate how relevant it remains in Japan - nothing to do with measuring potential sales. In terms of YouTube performance it's pretty similar to Splatoon 2 themed videos.