Apparently rumor has it that they are still including an optical drive too, so I won't get my hopes up regarding an additional drive bay (which I agree, SSD to boot and HDD for storage!)
As far as I know rumours either say nothing about the optical drive, or they say that is disappearing. If Apple do get rid of it it's highly unlikely they'll use that space as a second hard drive slot, they'll make the MBP slimmer instead. The only way I can see an SSD HDD combination would be if Apple had blade style SSD and a hard drive slot, but there is no evidence they are doing this so that would just be wishful thinking.