This may sound extremely bold for some of you, but keep in mind some things before posting below:

1- Super Mario Maker sold 2.68m so far (according to VGC)

2- Despite its good sales, the game released just 4 months ago (and more recent VGC data is yet to be released, so it should be higher).

3- The game has legs, it's a slow burner and is still selling well.

4- It's currently outpacing Splatoon's sales. 

4a- After 17 weeks on the market, Splatoon did about 2m.

4b- After 17 weeks on the market, Super Mario Maker is at 2.68m.

5- NX may or may not release this year. This should play a key role on this. However, I can see SMM still selling decently well even after NX's release due to it being a slow and poweful burner, much like Mario Kart or even Splatoon.

What do you think guys?

I still believe NX will be released after 2017. This year we will only have news about it.

That said, Super Mario Maker, along with Splatoon will probably keep selling as long as Wii U is selling. They are like essential games for the console.

So, 5 million is possible in my opinion.

If the Wii U had a longer life span, I think it would be possible, but since NX is coming rather soon, probably not : X

Whoa I didnt know the game did this well! I think its possible even if the NX releases this year because Nintendo may slash the the Wii U price to sell whatever is left in stores.

I don't think the Wii U will be replaced this year, still I think 5 million is pretty unlikely. Not impossible, but if I had to guess, I'd say no.

It'll be 3mil+ by end of 2015 (ship+digital). I can definitely see it above 4mil, as of 5mil it really depends. Nsmbu a launch game barely hit that figure. I know SMM is much better received but still!

I hope for 5mil

Ya it's certainly possible, probably depends on how strong it's bundled in the future but 4 million should be a given.

I'm thinking it will end up around 4.5 easily so yeah it's possible, I mean it's Mario

It'll be close, but I will guess at 4.6 million!

If it gets ported to the NX, then yes. If not, then no; not enough time.