For the DS, note that he seems to be targeting the original DS (e.g. not DSi OR 3DS). I remember there being some slightly better stuff but not significantly better than what he made.
The GBA version also looks pretty good on my DS lite (compared to games on the system). You can't rotate the camera though, so the dragon doesn't rotate. The monkey-head rotates on it's own though and looks pretty good. You're right that there are a few games that do 3D on the GBA, but I can't imagine it's fun coding wise since it the hardware support is basically zero in that regard. But there are some weird ones out there - Banjo Pilot comes to mind, which is a weird mode-7 3Dish flying game. Not exactly a great game, but pretty cool to see. Even with that game though, they have to sacrifice basically all terrain to be able to render the other characters at a decent speed IIRC, so the entire game is just flat.
And if you want to get really obscure, there is Faceball 2000 on the GB, which is a "FPS" and is 3D (And runs at like 15 FPS IIRC). There's no way you could render this scene on it though besides just pre-rendered sprites like was done with the GBA.
part of this album http://imgur.com/a/XQCEJ
http://www.ricedigital.co.uk/wp-content/uploads/2013/05/hunt...