The following comes from a PocketGamer interview with Terraria dev, Redigit...

"I am wanting to code Terraria 2 in a more portable language so it can be released on multiple platforms at launch or close to launch. 3DS is something I was very interested in getting Terraria on but the system unfortunately cannot run Terraria the way it needs to be ran."

There are plans to bring the title to consoles, so maybe a Wii U version could happen at some point.