I would imagine that there is a cost issue prohibiting a huge online venture, and I'd rather not pay-to-play. I really don't know too much about it, but I would imagine a peer-to-peer connection would be pretty cheap, comparitively.
NWC is just fine, most of the changes we want would happen on a software level. Mario Kart wasn't so hawt because you couldn't directly choose which person to play agianst. This has to be a software issue, because you could choose in Animal Crossing. Although I'm not sure about the speed of connecting to peers, I fear that that may not improve too much. Still, it's FREE, and that's the most important part.
While Nintendo is being secretive, I'm positive they're going to reveal most important stuff at E3, and only minor things after. They're probably envisioning tweaks and changes they may make, and I think they'll wait to reveal the definite pricing till after E3. We'll get enough new info at E3 to get the hype train started, and nothing ground-breaking will be revealed after. It seems natural to get the big thing out at E3, and then slowly get more specific with the details up until launch. Plus, don't forget games, details about all the games needs to be revealed, and there just isn't going to be enough time at E3 to do all that. They can afford to be plenty secretive, but they have to choose just what to be secretive about