Breath of the Wild is truly a beast. Well deserved sales. Hopefully it can keep the momentum going. As much as I like Ocarina of Time and Twilight Princess, it is about time that another Zelda game dethroned their sales.

Easy, now. I like to play optimistic as well but I have a hard time seeing more than 6 million units move this year. 

Zelda and Nintendo games in general are more based on "legs" than in first year
Look at Ocarina 3DS which first year sold 2.5 million and now it is still growing with 4 810 000 units

I like to be cautious as well, but Nintendo should announce 5m shipped + digital next month for its first 4 months (March/April/May/June). With another 6 months remaining this year and a full holiday ahead, 6m is basically garanteed at this point. ^^ 

Nintendo has BotW at 2.76 as of March 31st, VGC had it at 2.07 as of April 2nd. Right now, it's at 2.91 as of May 27th. That's an additional 840k of sales. Add that to Nintendo's number of 2.74, that would put it at 3.60, not counting whatever digital sales it accumulated within that time.
Let's say, hypothetically, that those 690k sales between Nintendo's 2.76 and our 2.07 are all digital (I highly doubt it, but let's go with it), that's 75% of its sales that would be physical. Let's say this game maintains that mark. Let's take this 2.91 mark we have no, divide it by 75%. That puts it at 3.88 million.
So as of May 27th, 2017, combing physical + digital, Nintendo + VGC, that puts The Legend of Zelda: Breath of the Wild somewhere between 3.60 - 3.88 million copies, sooo close to 4 million.
Nintendo's next press release, can't come soon enough!

splatoon week might see a bump for BOTW

Updated with week 13!

BotW is the clear winner again and this gap will only keep increasing. I actually don't believe I'll say this, but next week we can expect BotW to be up again. As for TP Wii, it will keep decreasing.

This is beginning to turn into a bloodbath. 
Twilight Princess drops to 59,601 units the next week and Breath of the Wild may very well go back over 80,000. 

If this keeps up, Breath of the Wild, on the Switch ALONE, will outsell Twilight Princess on the Wii AND GameCube!!

With digital will be easy win for the new zelda

Actually, this is very plausible. Personally, I expect BotW to sell 6m alone on Switch within its first year (7.5m combined).