I think we will see the basic bare bones with Super Smash Brothers DS. We won't be getting internet connectivity. However, this isn't a bad thing, but a good thing. Nintendo knows the abilities and weaknesses of their own protocol for wireless play. They can push the limits of game design by not jumping to online play with Super Smash Brothers.
Here is what I would like to see:
1)8 player multiplayer matches/4 player Co-Op mode.
2)Expanded Adventure Mode. How about top down dungeon for the Link themed level? Or a race for the F-Zero themed game? Something interesting and fun. Then sprinkle alittle Co-Op magic and you have an amazing Adventure mode.
3)Custom Challenge creations. Pick the level, Opponent, victory circumstances, and Computer skill level. Then see if you or you and your friends can beat it.
4)Larger levels. With a pontential for 8 players to play verse mode, some of the levels need to be designed for such large masses. I would love levels that are larger and have more pitfalls in the middle to spice things up and set up traps.
Zelda is still going to be 2D with the multiplayer aspect. Nintendo has created 2 really fun games with this multiplayer angle, but they haven't hit a grand slam with the game design yet. I fully expect for this game to really push the limits of the 2D Co-Op Verse gameplay design that has made the Zelda franchise fun.
I also suspect this will be one of those most own games that will push DS sales, and the experience will definately be worth it.