Just some things I noticed and surmised from the comments from that page; there'll either be no extensions that require a GBA slot (eg: guitar grip for GH:OT, Rumble Pak, miscellaneous other DS option packs) or they'll need to be repurchased for this new DS version.
I think I can see a bit of a parallel forming; remember how the GBA came out, then the SP, the slightly sleeker and sexier version, then the Micro with its lesser compatibility and relative uselessness on the market? Well, I can see the DS line going the same way; despite this DSi having more features, the majority of these features will be totally useless while mobile phones, iPods and the like are still common around the world.