Upload & Sell: Off
Let say Canon MKII is better than the old version, but the Tamon with VC is similar to the old one, then I'm sure it'll sell like hot cakes.
My guess is that the Tamron will better than their old 28-75 which was close to the old Canon. If it turns out to be better than the old Canon 24-70 in IQ, then I will have a difficult decision to make. In all likelihood the Canons will have the better AF, the area which the Tamron 28-75 was a bit slow. I can only guess that the omission of IS in the Canon means that the IQ must be better. Otherwise, why make it - lighter weight only wouldn't sell many lenses.
The choices we will have are a good thing and I can't wait to try them out.