And can't you use the DS as a controller in Pokemanz Battle Revolution?

It's there, it's just under the radar. That DS demo channel is coming out in America this year I'm sure, and new games are going to have to use it, because there's about a billion DS's out there. And the way we all got excited over the PictoChat stage in Brawl... there's gonna eventually be something like that. Maybe something like that or LineRider, where the DS player is drawing the stage and the Wii-mote player is doing... something on it.

 I think that is what you do when you download a demo from one ds to another. It doesn't really download rather than stream. 

The Ds-Wii connectivity is the ace under the sleeve for nintendo, But they have a lot of plans with the DS right now, as Iwata said on the beginning of this year

There's a Brain Age-type game on the Wii that allows you to use the DS as a pen to write essentially. I forgot about that one.

My Word Coach does several things. Of course, we don't even have DS demos in America yet, which is far my important!

I don't know if I really want such a connectivity. I mean, look what they did on the Cube, and back then they really tried... I can't think of much that would make such a connectivity really interesting, and the problem is that you can't make games basing on it because you can't expect people to buy a DS only for one specific game...

 Well there are already more DS's out there than Wii's. Besides who says you have to make a whole game around it, I'd just like something like the Tingle Tuner in more games. My brother generally sucks at games, so I had to be there most of the time he played the Winder Waker and the tuner gave me something to do and made it a little easier to point him in the right direction. Also speed certain fights sense I could lay bombs.

The Wii will eventually have its download station connectivity I would guess that Wii/DS connection would start to take off after that point.

I'm expecting the Wii/DS capabilities, but nothing huge. They've done it for the last 3 generations in some form but kept it pretty minimal:

Super Game Boy Player - SNES
Transfer Pack that came with Pokemon Stadium - N64
GBA Cable that was only compatible with about 3 games - NGC

I expect we'll see something around the 3rd or 4th year that'll be pretty cool and new but not much after that again. I think they'll only go big with the wii/ds connectivity in 3-5 games tops. And i expect all of those games to be Nintendo published. I wouldnt expect anything exciting from third parties using this. As someone noted above maybe just as an extra controller method or bonus for a second player but nothing really jaw dropping.

EDIT: I also forgot about the Gameboy player for the cube. just add that to the list above.

GBA cable only 3 games? I must have owned all 3 then: Zelda: Wind Waker, Star Wars Rogue Squadron 3: Rebel Strike, Final Fantasy: Crystal Chronicles.

But the Rebel Strike one was soo pointless, you could press a direction on the GBA D-pad to send commands to your R2 unit like attack, follow, other stuff, I can't remember. It was pointless because you could do the same thing with your GC D-pad. The only benefit would be discretion in multiplayer, but who cares what your opponent's R2 unit was doing, just shoot the guy!

Checked Wikipedia, here's the list of games that could use the GC/GBA cable:

 
And here is the list of GBA games that could use the cable, pretty much always in conjuction with their Gamecube counterpart: