The present six speed auto has been discussed to death, and whether it meets your needs or expectations comes down to personal opinion, preference, expectation, etc.
As I stated before, the Euro 2.3 diesel already matches power and torque of the larger 3.0 diesel used for US market, and is lighter and more fuel efficient. Even if Fiat could fit a 3.0L inline six in a Ducato, what would they gain? Smoothness for certain, and maybe added durability, but would that justify the cost when most other companies are downsizing engine displacement? I don't know but expect it would only be needed if a new Ducato was made larger and heavier-duty.
By the way, typical torque ratings of 3.0-liter modern diesels are in +/- 450 lb-ft range, which I believe exceeds torque capacity of existing ZF 9-speed. The 2.3 diesel's torque is about all the ZF is rated for. And I'm not even sure other factors like much higher GCWR of a large and heavy van wouldn't rule the ZF out anyway.