I think they failed because they were designed to run on the DS/DS Lite. Obviously the DSi isn't just a new model of the previous DS's; that is, there is new code in the firmware. I don't think Nintendo has stopped us flashcart users just yet.
Of course theres new code in the firmware, it has a completely different menu with new applications and code to run 2 cameras etc, it would have been laughable if any of the current flash cards actually worked. However flashcards failing doesn't really mean anything at this point in time.
A custom or hacked firmware installed from either SD slot or over wifi via a server side application would be lovely. If the firmware can be updated over wifi, it could be possible to make the necessary changes to the loader to allow it to boot old flashcards again, but i'm just guessing and assuming things at this point in time, just like everyone else..
I've read about yasu managing to run code from the DSi but he doesn't give away how it was achieved and what the limitations were, so this hack is moot until further details surface. This is why i haven't made a news post about it because theres nothing to say other than watching a 5 second video and guessing and assuming about something most of us honestly know nothing about yet.
Hmm, yeah. I, too, felt Yaso's video showed very little in the name of details as to how he/she managed to write "Everyone's First Program" (seriously, it doesn't matter what programming language you learn, the first program is ALWAYS "Hello World"). From the specs we have, I'm guessing Yaso ran some C/C++ code through the SD slot, since we're still working with Arm7.
Honestly, I'd hate to see us having to work around things with the DSi in the same way that homebrewers/pirates have to work with the PSP (putting a service-mode battery in to run code from the memory stick). But, if it comes down to that, I'll do it.
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Currently running: NDSL: Unflashed (No FlashMe) Slot 1: Official R4 running Wood R4 1.27 Slot 2: eWin w/ Rudolph's GBA Loader v0.57 Roms: Untrimmed