I've lost a lot of interest in this game since it's release. A couple of month ago it was a must buy but unless it's truly the definitive version I don't see me bothering now all the hypes dissipated.

I doubt there will be much promotion for the Wii U version. It's not like Nintendo are going to release a Nintendo Direct for it. They should do a direct if they are serious about attracting third parties and they could tout any gamepad features this version might have.

I reckon it'll have the weakest framerate of all versions, have a few ok (but not ground breaking) tablet features, and sell less than 200k.

They may not have any of the console or gaming PC as you mentioned.
However Watch Dogs was also released on PS3 and Xbox 360. A lot of people likely own these consoles and would have bought it for them instead.
Those who have waited have probably lost interest in the game as their is really no hype behind it whatsoever now. Chances are they will buy other games over the holiday season, as the holiday season consists of more solid releases. 

The Wii U version is being released far too late, has no hype, Watch Dogs itself as had average reviews, and other games more appealing to the Nintendo audience will be on offer.

It is a shame, but sadly these seem to be all realistic factors in Watch Dogs not meeting good sales on the Wii U. 
Honestly it would be a good thing if hypothetically; the game is a massive success on the Wii U. If this was the case, it would almost be guaranteed that Ubisoft would either create a late port of Assassin's Creed: Rogue or Unity. If not a late port, it may guarantee the following installment of the Assassin's Creed franchise.

This is all merely just speculation on my part of course.

It will sell at least one ;)

I will wait till it hits budget price, but knowing the trend of Wii U third party title prices dropping like a rock, it shouldn't take long. I think the gamepad will be a good fit for this game. Kinda done with my 360, and I'd rather get the better graphics at (probably) a lower price. My PC MAY be able to handle it but I'd rather not take the risk. 

Anyway, in regards to the topic: I'd say about 350k.

Buchares team is pretty decent, specially on the technical stuff but they are not so good on the gameplay parts, that is why they always work with other teams, and never by themselves. They have experience with the Wii U as they worked in ZombiU, and that may go in favor of this title, the scenario, plot and gameplay elements are all done, so they really need to focus on engine improvement and maybe some gamepad integration, I hope they got good results.

100k.

This is pretty much the answer that I was going to give.  I don't think that it will be released and if it is, not many more than 0 will buy it.

this game is going to get horribly overshadowed by the Ninty stuff on the system. If it hasnt release by now its screwed. 180k

I'm honestly surprised you didn't pitch it lower. I can't believe you're being more optimistic about a Wii U thing than me... XD

i imagine it will hit the bargain bin pretty quickly, and I imagine that they will actual do something with the gamepad otherwise why else would it take this long? if not then its screwed

200k-300k copies if it doesn't get cancelled that is!