at $699, hell no, it will def be twice as faster than a rx 570 but not 4 times. You can buy a new rx 570 for as low as $180 x 4 = $720.
You need to take electrictiy into account. At 7nm it will probably consume very little. 4x 570 consume a lot. They are not even profitable atm.
I will probably buy one to play around with it. More depends on the results.