i dont see it getting to 600 in less then 2 years maybe 3 this type card price willl depend more on what comes out from befor or shortly after it 6990s and 5970s held high prices for years after their release. It will be limited release likely like most other dual gpu card so holds its price longer with less of them in the market to buy.
And what kind would that be we been using opencl for ages for mining of all types its how all amds been mining sence they stoped using cal 3-4 years now.
Before the mining craze a 7990 was $499. Are you forgetting that?