Canon USA still lists the 'estimated retail price' as $1399. But street price is determined by supply and demand. Supply is short. The impending discontinuation of the MkI means that soon, the $2300 MkII will be the only 24-70/2.8 available new from Canon. That means demand is high. Low supply + high demand = rising prices. Simple, and as many have pointed out, this is exactly what happened with the 70-200/2.8 IS.
The increases trickle down to the used market, too - only recently, two years after the 70-200 II release and after street price has fallen a bit, are used copies of the MkI coming back down into the range where they were before the MkII was released.