True, but every once in a while I enjoy using my DSi, just because its part of the good old days of the original DS, and I was thinking of learning soldering to hardmod it and install sudokuhax later. I'm just scared because I can buy sudoku now, but if I mess up the hardmod then it's game over because I can't get it on another DSi.
Then don't solder. You could find a piggyback adapter *or* you could use conductive glue if you're not very good with an iron or you don't have precise equipment. Alternatively you can send it to someone who does this sort of thing professionaly, there's plenty of options.
You're missing several steps in this equation. Soldering would give you access to the NAND which was patched out in later firmware revisions (hence no more Hax), that in turn would give you access to the keys (provided you connected to the shop at least once, otherwise your system didn't generate any) and that would allow you to sign software. You'd still need some source of unsigned DSiWare, decrypting tools etc., and we're not quite there because the 3DS stole the thunder of the DSi hacking scene. I feel that whatever's on the store will be lost forever.
A certain shepherd site has all the dsiware dumped so preservation of dsiware really isn't an issue now.
