Just to go off on a tangent a little bit... Nintendo is only really succesful as it really is because they target people of all ages and not just hard core gamers. Nintendo focuses more on delivering games that will appeal to everyone and thus I believe that nintendo is kept plenty busy doing that, so they neglect the hardcore gamers.
360 and PS2/3 develops games that hardcore gamers really like. Hardcore gamers I think have a hard time trying to get into some pretty simple ideas that nintendo has made such as the brain age and wii sports stuff. They just aren't that fun, but they do have appeal to everyone else.
Now with that in mind, Smash is one of nintendo's few series that actually appeals to those hardcore gamer pretty well and taking off the project deveolpment seems extremely unlikely. Mario is getting pretty old, but they keep coming up with new ways to introduce him. Pretty much smash has become a name just as renowned as pokemon and Mario (weegee gets left behind again xP) only it's not something that you can spam multiple project delevopments on, so I think Smash will be a continued series so long as new gaming consoles come out.
For now, I wouldn't except any smash developments for a good longggg time. ssb64 came aroudn teh middle of 64s life time. melee at the beginning of Game cubes life time and brawl the same with wii (pretty early). So I see another Smash game coming out in probably 2015 when technology gets good enough to start another wave of Home Console gaming.
The DS on the other hard is a different matter. It would be a pretty big development and staging point for nintendo I think as they have never done a fighting style game for there handhelds that was developed by there 1st or 2nd party people. Most of there handheld names are strategic or something like that. At the very least outside of japan. They have developed real time fighting games before like Tales of the Tempest or something like that. I pretty much view the idea of handheld Smash can go either way 50-50.
Has anyone else heard that rumor about the "Brawl Channel" where you basically can download stuff for brawl to play with. If you haven't just google it and it will tell you. I have no idea of that was a hoxs or not, but I still think the idea has some merit. It seems possible as microsoft has done that with there games and it would be a money chance for nintendo why not take it. Although since nintendo I think hasn't done something like that before it's most likley not going to happen. But you can never be too hopeful