In the same tweet that Kobayashi announced SB was back on the US eShop, he said "Europeans wait a little bit longer!" Or something to that effect. So they've been working on it this entire time,they just haven't said anything.
Patience is key.
Your MML string needs to be in a labeled DATA block that ends with DATA 0. For example:
@SONGDATA
DATA "mml string here"
DATA 0
Then you have to use BGMSETD to load it to a BGM track. Such as:
BGMSETD 128,@SONGDATA
The upper display is actually 800x240, but that's only for the 3D so it can draw two images. The display hardware draws 2D images to the screen at 400x240 but renders polygonal graphics at 800x240 in 3d mode, which is why 3d looks a bit better
Your Android calculator just pretty-prints the result. Internally, both Android and SB use the same floating-point standard: the IEEE 754 double. The Android will get the same result as SB (at least it should, or something is very wrong), but most people don't want to look at a number that long so it makes it look fancy.
Of course, you may have known that already.