N-Nation (not the same as NintendoNation) scored a nice little interview with Lisa de Araujo of Creature Labs, and here's what she had to say:

The Game Cube version of Creatures is actually being developed by Swing Entertainment GB, to whom we've licensed the title. They are also creating a GameBoy Advance version of Creatures and on that project I can say they're making excellent progress. The Game Cube version is entering development now, having been through a lengthy design phase and as such, I don't have a release date for it, however, if I can get some better information from Swing, I'll be sure to pass it on. The internet connectivity has also not been confirmed (or denied!). Creatures is a popular and long-lived license and as such, I expect it will do well on console and handhelds. Hope this helps!