Honestly, this is probably a pretty good week to launch a game on WiiU. You can be relatively certain that Smash's release will sell hardware, or cause owners of the system to turn the thing on for yhe first time in a while. So eyes will be on the eShop or the Nintendo section at Wal-Mart/Gamestop/whatever.
And regardless of the game's successes or failings as a GTA-alike, its only peer on the system is LEGO City Undercover, so people who don't have an Xbox or a Playstation could well be itching for that sort of game.
Plus you have Christmas shoppers who are looking for WiiU games and thinking, "Watch Dogs? I've heard of that! I bet Billy will like it!"
I doubt the game will be a multi-million seller and it certainly won't change Ubi-Soft's mind about publishing on the WiiU, but I bet it does okay. But these are the opinions of a man who knows precisely jack about business, so I dunno.