The DSi XL has quite a bit of free space inside to be honest - to fit the USB C charging and Bluetooth audio you shouldn't need to make shell mods other than to add additional buttons. The speakers would have to be in the top half of the console, which I am less familiar with. I've personally...
Hi, I'm a person who mainly does hardware mods for the Nintendo DS consoles, not really into Wii stuff at the moment, but it's on my to do list to make a Wii portable or Wii nano. I probably will post a couple guides for some DS mods up here in the next couple of days