I try to keep each of my designs as focused as possible. This was a game that was designed, from the ground up and all the way to the end, music and all, around the DS platform. I studied the platform carefully, and thought about the "perfect" game for that platform, from my point of view. Diamond Trust is that game, and it simply does not exist separate from the platform.
When people toss around the word "port" so frequently in our world, they act as if platform doesn't matter. Platform matters! At least to me, in the way that I approach design. My next game (unannounced) is designed around internet-connected PCs. That design is very different as a result, and it would never work on a DS or even an iOS device.
This may strike some people as a strange, rigid way to go about making games---picking one platform and going full-bore on it. But I hope that other people appreciate and understand it.
So, the short answer is that if I was going to make an iOS game, I would design an iOS game from the ground up. Diamond Trust will never be ported to another platform.