So I decided a hardmod wasn't worth the trouble and just got my brother to buy Sudoku on my old 3DS so I could use Sudohax. Works like a charm (after having to retry a bunch of times; thanks for error 014-0062, Nintendo - why is this so damn common during system transfers?)
I should warn people: I've already noticed the circle pad on the New 2DS XL marks the top screen just like the original 3DS, though thankfully, I don't think the touchscreen bezel scratches it like the original model does. Hopefully the circled doesn't actually scratch it over time like the old 3DS, but I wouldn't be so sure. It's also, one again, a huge, shiny fingerprint magnet, which is a real shame.
It's definitely a bit cumbersome, but ultimately, it's far better than the stupid ideas they had for the New 3DS (XL), so at least it's an improvement over that.
Screw you guys, you get everything else. At least let us have this one shitty victory. I still want my exclusive Yo-kai Watch medals, dammit. We never got them over here...
Using the DSiWare boot injection (w/system transfer) method or a hardmod, yes. No hardmod has been detailed yet but it should be completely possible. I was going to open up my brother's and have a look, but I probably shouldn't since it's not mine to tinker with.