80% sulphuric acid contains more water than it contains sulphuric acid, which is to say, it won't react with any additional water.
There is only H2O, HSO4- and H3O+ in it, and as far as I know HSO4- isn't that strong an acid. At least not strong enough to bind the reast of the water.
If 80% sulphuric acid would work to dry ether with, it wouldn't have mattered if they were miscible or not, as you still have to distill the ether when you're done (leaving H2SO4 and H2O behind).