What I'm curious about is what the backwards compatibility situation will be like if Nintendo indeed uses Tegra 2, or really anything "Gamecube level" like the rumors have specified.
Nintendo has already announced that 3DS will be backwards compatible with DS. Until now Nintendo has only implemented previous-generation backwards compatibility with compatible hardware, and with the current generation (DS and Wii) Nintendo has done this by augmenting the previous-generation hardware (GBA and Gamecube, respectively).
If Nintendo chooses to augment existing hardware again then it won't be using Tegra 2, or any third party IP for that matter. I also think that the basic DS design has some limitations that will make it difficult to scale significantly. ie, I don't think that it will be bumped from 2048 polygons per frame to over 100,000, which it would have to be to really be Gamecube level. This is also not taking into account the need to render things twice for stereoscopic viewing.
Another alternative is redundant hardware. Nintendo could be including the original DS 2D and 3D hardware, but I doubt this because it'd be all but useless in conjunction with a much higher end GPU. So I think it'd be a waste of die space.
Finally, there's software emulation. It's not that much less likely, but I think Nintendo would be introducing compromises, especially if they tried to emulate it with the 3D hardware of the 3DS. I'd be pretty impressed if they actually pulled off an emulator so soon after Tegra 2 would have been sampled, but it's certainly not impossible. If Nintendo has done this then it'd be a good indication of what other handhelds can do.