In its list of Japanese software that supports the Circle Pad Pro (Slide Pad Expansion) on the Nintendo 3DS/3DS XL (3DS LL), Nintendo cautions that Super Smash Bros. for Nintendo 3DS will not support the accessory. The same document notes that the New Nintendo 3DS and New Nintendo 3DS XL do not support the Circle Pad Pro, but added that the new systems' C stick and ZL/ZR buttons provide similar functionality built-in.
Super Smash Bros. for Nintendo 3DS will debut in Japan on September 13, followed by North America and Europe on October 3.
Before all the "lol Nintendo stickin' it to Gateway" conspiracy theories, I truly believe this is just a money grab.
It could likely be reasoned that this is because the CPP covers & uses the IR port and therefore will be incompatible with the Amiibo stand, which will be used in some way in Smash Bros. 3DS, but Amiibos are usually not something you'll be taking out on-the-go anyway -- and on-the-go gaming is pretty much what handheld gaming consoles are meant for. Thoughts?
ARTICLE SOURCE [animenewsnetwork.com]
NINTENDO SOURCE DOCUMENT (JP) [nintendo.co.jp]