Nintendo is highly protective of their IP, so I don't think they would even consider releasing those games on other platforms.
And where did you get the idea that emulation is illegal? It isn't. If you don't own the physical media, then it is, but if you do own the games, there's nothing illegal about it. For years I used the No$GBA emulator to emulate some of my DS games and they worked fine.
I'm not really into the Pokemon games anymore. I used to play the Diamond version on the DS a ton when I was a kid, but that was the last one that I truly played. If I were to play them on modern devices, I would much prefer the ability to use a physical controller. I'm not very good using on-screen controls.