I could definitely see Metal Sonic getting some spotlight soon. With all the video game references, we got a lot they can use as far as Meta Sonic goes.
"I ain't gonna let it get to me, I'm just gonna creep, Down in Pumpkin Hill I gots to find my lost piece. I know that it's here, I can sense it in my feet, The great Emerald's power allows me to feel."
It's not really for any advantage, just something extra you can do with Smash. And yeah, they will interact with more games in the future. I just like them more for the collection purpose honestly...
Customization is already in the game... they are more like your own little CPU you raise which you can customize and such. You don't actually play as them or anything.
They are new NFC figures that you can train and level up to fight with or against in Smash. These links explain it a lot better... lol
http://www.smashbros...wto/entry8.html
http://www.nintendo.com/amiibo