I agree in that I think the Wii will follow the DS 'upgrade' model. They will NOT drop the price - at all - until sales significantly start to dip.
Then I think you'll see a 'Wii HD' or 'Wii+' released at a little over the current price point. Then the Wii will get a price cut at the same time, and most of the Ninty fans will start upgrading.
The amazing thing with the DSi is that DSi games will NOT RUN on a DS!! So it really is a new handheld (it has extra RAM, as well as the camera and other features).
The Wii+ could follow the same pattern. I'd love to see the next Wii go back to carts - but this won't happen for the Wii+, as backwards compat is so important (it must be able to play Wii titles).
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I'd expect lots of onboard RAM, and special Wii+ (only) downloadable titles. Its a great way to migrate to a DL-only world - have the retail Wii titles, and the online only Wii+ titles.
They *could* stick extra VRAM on it, extra RAM, crank up the clock speed on the GPU/CPU, upgrade the output to 720p, controller will come with M+. Even a 1080i upscalar and/or HDMI plugs, or better FSAA. Lots of options really.
Opens the door for them down the track to release a ultra-cheap Wii+ WITHOUT a drive (might be half the cost, if not less) - DL titles only. By then they would have a good catalog of DL titles.
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Doesn't anyone think it wierd that Ninty have NOT released any really significant WiiWare titles of their own? They have obviously been working hard on DSi titles - but I wonder what else they have coming. Or maybe they are leaving it to 3rd-parties for now...