Alex Sora 89 here (theory partially suggested by my girlfriend Faith). Basically, the only reason Mario must get one million coins is in order to pay a ransom for Peach. There's gonna be a Bait-and-Switch near the endgame, when it turns out the million coins only grants the player access to the final castle, and then the game goes back to the series' roots: an old-school showdown against Bowser. That's because Bowser betrays Mario as soon as the latter gives him the cash. Calling it right now.
- Jossed. Getting a million coins is completely non-essential to the plot, and actually doing it just gives you an alternate title screen.
Seriously - think back to Mario & Luigi: Superstar Saga. Remember the insane exchange rate between Mushroom Kingdom coins and Beanbean coins? The conclusion is that the Mushroom Kingdom's economy is a hyperinflationary nightmare.
And now, a particularly dickish Bowser (or Ludwig) has contrived an evil plot to flood the Kingdom with gold-coin-making Power-Ups so Mario and Luigi will unwittingly drive the Kingdom into an economic black hole from which it will never recover.
As the greediest character in the Super Mario franchise, I refuse to believe the he won't think to steal the one million coins from Mario while the plumber is busy with Bowser.
It just makes sense, doesn't it? The greediest character in the franchise charging the players to have him appear in the game he would practically kill to be in.
- Except, Nintendo has confirmed that all DLC will just be additional Challenge stages.
