My oh my, it is just spoiler heaven up in here. This is precisely why I always stay away from gaming forums when playing a new RPG.
Anyhow, I just thought of a random idea... What if Shulk's moveset involved the Talent Gauge? It could function somewhat similarly to Little Mac's Power Meter. Every time Shulk lands a hit with a normal attack, the Talent Gauge builds up, and when it is full, he will be able to use a selection of Monado arts. Said arts could have Monado Buster, Monado Shield, Monado Speed, or Monado Eater.
Also, I was thinking for the 3DS version, the Xenoblade stage could be Prison Island. The shackled giant could be in the background, and Metal Face could be a stage boss. As for the Wii U version, I would love for it to be a dark, stormy stage where you can see the two titans fighting in the background. Perhaps the players could fight atop a platform that circles around and weaves between the two titans. That would definitely be a unique and iconic stage in Smash Bros, in mine opinion.
What say you lot?