The bottom line is this
'IF' sm4sh has cpp support there WILL be gc controller mods. No way around that. If it's possible, people will mod their 3DS for this, me included.
less likely but still QUITE probable is the chance of 3rd party gc controller adapters. (I'm not sure of the LEGALITY of this though)
even less likely and less probable would be if Nintendo released an official gc controller adapter.
If there is no CPP support for sm4sh3D I will be quite upset for these reasons
1. I don't see any other possible way to mod the controllers into existence
2. no c stick. gives sm4shU a totally different option for strong attacks than the sm4sh3D players. I'm sitting here playing with the controls and it seems pretty hard to execute a smash attacks the same way i would on a gc controller by tapping the control stick and holding the button
For some reason I've started playing super smash flash 2 lol. but anyway the control options really intrigue me.
I use joy2key to emulate my 'gravis gamepad pro' to my keyboard, it's a pretty bad controller i got it cheap at a thrift shop cause it had a USB plug and that's all i could find, it's basically an original PS1 controller w/o the analog sticks.
here are my problems with it.
1. I've set up the four button layout like i assume smash will be like: A on the right (normals) b on the bottom (specials) and x and y (jump) on the top and left. I've been playing for about a week or two and every time I pick up that dumb controller to play a silly flash game (It's actually a pretty nice game, emulates brawl quite well [except faster xD]) it still feels unnatural and uncomfortable.
2. the one thing i do like about the controller is the nice trigger buttons, it's got four trigger buttons just like the PS1 controller. I've mapped shield to L1 and R2 and grab to R1. even though these are good quality trigger buttons, I find myself NEVER using them. this comes from a player who came in from brawl and my MAIN and pretty much ONLY strategy was to shield and roll around grab pummel and throw. after brawl and i found project m and became more of a fast paced player i still used Powershielding shieldgrabbing and normal grabs as a huge part of my strategy. and it's not the games fault, the shield is maybe even more useful in SSF2 and the grabs of my favorite characters are quite an advantage. I mainly don't use them because it feels unnatural. In a fighting game situation you want all your options to feel natural or you won't use them. comparing these trigger buttons to the 3ds triggers I like my 'gravis gamepad pro' triggers a lot more than the 3ds triggers. and I feel if i'm right about this whole unnatural feeling triggers thing I'm rambling about then the majority of 3DS players might not use shielding as much as if they were playing on a wiiU. That, combined with a lack of the c stick would make sm4sh3D play and sm4shU play SO much different.
as far as casual playing goes, I have tons and tons of fun playing SSF2 on my terrible controller. and I assume playing sm4sh3D on a terrible controller will be just as fun, for people who will take it that way.
I'm a very competitive person living in a practical ghost town when it comes to a smash scene. the 3DS' portability and online play is just what i need to:
1. revive my areas scene
2. play online when i fail to do number 1
and as far as competitive play goes, the 'gravis gamepad pro' WILL NOT cut it. neither will the 3DS default controls. So I sincerely hope the 3DS has CPP support and there are at least third party controller adapters. sorry for that wall of rant lol.