So, there are quite a few technical reasons as to why we can't really port over to the GBA.
Even if we used cross-platform libraries, or just converted the whole game over, we're talking about a system that's been obsolete for about 10 years. We'd have to curb back the audio and visual quality in order to fit on a tiny GBA cartridge. It's true that GBA carts can go up to 32MB, but that wouldn't be enough for Chrono X.
Game developers are just storytellers in a different medium. Our art team does an amazing job at conveying emotion into the tiny sprite style that we have. Remember all those little details you saw? The neat little world building tools like this "^o^" face? We hope you did. Sadly, we'd have to consider removing neat things like that in the complete game. While in of itself, it wouldn't be a problem, it's just there are a lot of little liberties we took that add up.
To further illustrate, here is one of the best parts of Demo 4 -- where Lan used the hammer to destroy the speakers. We took the time to animate the destruction of the speaker as Lan repeatedly smashes it. While this could be done on a GBA cartridge, you have to keep in mind the developers stuck to a tiny 8 MiB cartridge, in under a year. Can you imagine trying to balance between space and animation quality?
And there's gonna be neat little things like that sprinkled throughout the whole game. It adds up to a lot of extra work after a while, but I think the story experience will be worth it in the end. A lot of sacrifices would have to be made, and it's still very possible to get stuck if we overlook something. We'd almost have to start from scratch..only to deliver, in my opinion, a less complete experience. While it might run okay on a GBA after much trimming, emulators would have an issue running aspects of the game. It'll never be as good as developers with official development kits.
Factually speaking, more people own a PC/Android than the GBA, so it just makes sense to develop the game on there. Since many people carry around their own mobile device, they would have to lug around additional hardware just to play our game. This becomes less and less of a viable option the more you think about it.
Now, you might argue that emulators have video filters, or hamachi connectivity, or save states, or whatever else you can think of to justify the extra work. But, did you really have all of that when you were playing your Game Boy in the car? Or at the park? At school when the teacher wasn't looking? No, of course not. Chrono X will have some video filter support in upcoming releases, and no need for Hamachi to handle the backend for multiplayer, but really, what would be the difference between an emulator for your PC, and a standalone executable file? There are less issues with the standalone executable.
The only reason I can think of to have our game on the Gameboy Advance is nostalgia. Nostalgia can't be the sole driving factor. We all had fun playing Battle Network on the GBA years ago. Those are some fond memories that I'll cherish. But that's exactly what they are: something to remember, not something to live in. You might argue that making a fan game like this is precisely "living in the past," but remember that we are telling a new story with new characters, places and experiences. We aren't shutting ourselves out to new possibilities and experiences. The development team is in complete agreement on the decision to not port to any classic handheld devices. That's what the Android port is for. It's to give you a fond reminder of the past when you played games on a handheld device, but to also keep up with the modern era.
Final note: we also looked into porting it to the Nintendo DS a few years back and we met with similar issues. Needless to say, we abandoned the idea. We want our game to be the best it can be, and the only way to do that is to go forward.