The hole you refer to is the stowage shelf, which I agree, isn't much use, as most things get thrown out under acceleration!
It is not quite the right shape for a DIN-sized unit, because of the rounded bottom edge and there has never been anything other than a different type of stowage shelf (one with builtin seat heating controls) available.
It is deleted if a double-DIN audio unit is specified and an alternative tray in front of the handbrake is fitted instead.
The other thing which foxed me for ages was the apparent square cut-out on top of the dash, above the central vents. Was it for a pop-up screen or something?
No, it's for nothing at all, except aesthetics!
Cheers,
Mike