Can the GBA version be a playable console?

The answer is no, because in terms of gameplay, it is extremely different in terms of gameplay from the other consoles. Compare this video (http://www.speedrun.com/run/9mrll24m) with this video (http://www.speedrun.com/run/1zq2q58z). You see how different they are?

For this reason, the GBA is simply listed as a separate game here: http://www.speedrun.com/lswgba#All_Episodes.