Without a rail / metro link between them, it would be very difficult to operate 2 Dubai International airports satisfactorily for inter-line transit passengers. And the proposed metro line has not even been started yet. In fact, not even contracted.
Road connections are totally inadequate.
I've also heard that EK intend to stay behind where they are now for many years.
My guess is that the opening of the new one will be delayed again - and that it will be a very long time before it eventually builds to anything like the mega-hub it was intended to be.