WiiWare is currently the only platform, though Provinciano noted that he was currently "in talks" with Microsoft on bringing the game to XBLA. PSN was also on the table, he offered. A PC version would be out of the cards for "at least a year."
Provinciano began the game as Project Grand Theftendo, where he sought to create an 8-bit version of Grand Theft Auto 3 that ran on the NES. We'll have a preview of the game soon.