Answering how much more 'should' it cost, I'd say $700 more.
the 70-200 f/2.8 without IS cost, $1300, the same lens with IS cost $2000. So all the tech can certainly be accommodated at a 'pro IS level' with a $700 up-charge, maybe a touch more if they want to add special coatings of what not to the is lens element.
I am curious how and when we collective believed that it costs Canon $400-700 to add IS. I mean really?
It probably does not cost $50 in materials and I am stretching it. The R&D is sunk cost anyway... Add another $30 per unit for re-tooling; retraining Other overheads and you do not cross $100 for IS...
Canon "does" charge a premuim for it, but we the consumers put a value of 700 on it when we should probably not... I had so much hoped that Tamron would resolve their QC issues (AF lens falling) that people would begin buying more of that great value at $1300.... and knock some sense into Canon.
Anyway... I'd be willing to Pay $1700 for it. Given Canon's better IQ and QA.