It would most likely be the originial Smash witha few new characters and online. And it would sell like hotcakes. Everyone bought Jump Superstars because it was similar to Smash, think of what Smash could actually sell!

What do you do with the second screen? Map overview? You don't have to actually use it for anything, but you do need to put something on it. I don't know what you could put down there that wouldn't just be distracting and hurt the game overall.

Maybe it could tell you where items are on the stage, instead of zooming out when an item comes?

The second screen can just be an extended stage or they can add something else.

Realistically I dont see them making a SSB for the DS, but for the Gameboy Evolution.

 zooming in????what the heck? why would u need to zoom in to see an item

I think the second screen could simply be used to displaying stock/time left 

yes, yes I would.

I didn't say zooming in, I said zooming out, like in Brawl, when an item comes down, the screen zooms out, so you could see where an item is. The DS screen is small, so if it zoomed out, then the characters would appear even smaller than they already are, which wouldn't make sense to me. It would be harder to make out what was going on. 

I think it would be a smart move financially, but I personally would rather wait for the next handheld for them to do it. The DS doesn't seem to be that powerful. I've played some 3D games on this system and it seems to demand a lot, with sacrifices made to get it working. Are there any games out for the DS that can prove it could handle something along the lines of the original Smash Bros. I'm not saying this is necessarily the case, I really just don't know, I haven't played any. If they do make it though, here's how I would like it:

Top screen used for on screen action.

Bottom screen used for inputting moves. If anyone has played Bleach DS, you'll already know how to make a fighter work on DS. The bottom screen can have buttons that correspond to different moves which need to be pressed by your fingers. This allows you to use physical buttons and touch screen buttons without having to hold the stylus. 

I would keep the roster small so it's not too demanding, from 10-15 characters. A lot of modes, weapons, trophies, and such would have to be cut, but online would have to be a must as would download play.  

To be honest, I'd rather have them make a next Smash in the next generation than doing it so soon. Infact, I'd rather much have Brawl as the last Smash Bros game (for the sake of ending the damn speculations (speculations as in the ones that are too unrealistic) and retards from places like....I don't need to say it).

Plus, doesn't Sakurai hate it when people expect him to do more sequels? (Don't bother saying Sakurai doesn't need to make the new smash game. Even Nintendo thinks it wouldn't be the same without him.)

This is just my opinion though, not to shot down anyone else's. 

Although I own Mario Kart for GC/DS, Zelda for GBA/GC/Wii/DS (series which were ported long ago to handhelds), I think in the long run both - Nintendo & Sony - would risk to harm some of their most important IPs by porting ALL series from stationary consoles to handhelds and vice versa.

I think it's a good sign that Nintendo didn't do a handheld port of the Smash series up to now.

Vice versa it wouldn't be the best idea to port Nintendogs to Wii.

I think (or let's say I hope) they are clever enough to keep at least one of their top selling IPs on Wii/DS exclusively (at the moment Smash/Nintendogs).

For the very same reason I think Sony shouldn't have started developing Gran Turismo for PSP at all.

Just my opinion.