Actually I have a Smash game in my DS, is JUS.

 probably because in an interview, the developer of SSBB wants no part in a DS version of SSB.

 I can actually see Sega making a similar game on DS than Nintendo doing it.

 No doubt it will sell millions. if it has wifi play

I have, it's called Jump Ultimate Stars.

JUS is not Smash. As cool as it is, I need me some 3D polygonal fighting with more physics involved.

Smash Bros DS could have similar graphics to the N64 game, though surely they could do better, as the DS is definitely stronger than the N64. And it has way more storage, so it could have plenty of characters and stages.

WiFi would obviously be possible for up to 4 players, and a create-a-stage with stylus controls would rock, but storage issues would probably hold that back.

It's definitely possible. I just think Nintendo will never do it because they want Brawl to be the main attraction and don't want to whore the game out too much.

well....maybe a SSB will come out for the Ds's successor - then it might have more buttons, better graphics capabilities, and *gasp*, maybe even use a disk for more storage.....

People who say not enough storage. Some ds cartridges go to 2gbs which is 1 less than the gcs disk.

 There are plenty of buttons.  All you need is a D-Pad, an attack button, a special button, grab, and throw.  The only thing you would lose out on are the taunts.

My only problem with it would be that the screen might be too small and you could lose your character pretty easily. 

If the controls are good, I would certainly buy it. I've never played mario basketball, but using the stylus for the Final Smash seems as if it would be too difficult/awkward, since I assume that it would mostly be D-Pad + face buttons. There are definitely enough buttons to make it, and make it well. But, who knows if Nintendo is thinking about it (it would certainly bring in a lot of money for them if they did, and would make a lot of DS owners happy = win for both).