Well, I have some reasons to think that.

First, I think you saw the photos I posted when pre-orders opened in Japan (Comg apart). The promotion in shops was huge, like a big release. And i could see a lot of people interested in that game. Now the promotion keeps being big, all the main shops have smash on their TVs and stands.

After that, I read some retailers blogs (GamesMaya, Osakaking, Sinobi...), and they said pre-orders started strong. One of them even said that pre-orders started stronger than Youkai Watch 2. 

Then there's Amazon.jp (pre orders closed already).

Finally, Media Create Ranking is showing Smash Bros for Wii in the Top 50. That's because there's hype for the game, and some people can't wait, so they're buying the Wii version while they're waiting for the new game.

Any of them is a source, just impressions. But that's my bet.

WOW! I knew about Amazon (keeps selling out) and here on COMG its almost matching nintendo's big first party games in pre orders (excluding pokemon obviously :) 

A million is definitely possible. I think as of now, 500k is a lock (so far). Lets hope it gets a million. I've been saying SSB 3DS could be very huge as every player will need their own copy (SSB is heavily multiplayer so it makes sense). I kno the WiiU version is coming out as well right after. It would of been better if WiiU+3DS version was spread out by a year imo (of course i dont want that, i mean if they were developed at different times).

Well at least we all kno SSB will be huge! 

This is actually something I didn't consider. With consoles, each players doesn't need the game, but with 3DS each person who wants to play needs their own copy. Should lead to slightly inflated sales, much like you see with hunting games these days.

You should add the User base of ach consoles for when relased the game and for the most recent comparison date. I'm sure PSP didn't have half the userbase as 3DS for when MH released, And if YW can be become a system seller we'll see after the next release, because the first one sold with the mouth to mouth and other marketing strategies (anime and mangas), and sells for 3DS haven't sold as great as last year to date, hardware wise.

Second, Monster Hunter wasn't a new IP on PSP, was a port from PS2.  It had already a fanbase. +600k sold in japan only for MH2 , growiing from +280k. It just became massive on handhelds...

Is it just me or the lacking of Hyrule Warriors at this point on the charts is a little worrying?

I was expecting it to pop up a little earlier.