Maybe when they're finally done with the A380 Airbus' engineers will get to develloping the A330 cargo... Let's hope.
If I remember correctly, a military version of the A330 is also planned, as a freighter/refueler...
It'd be interesting to see how a A320/321 cargo version would perform, sales wise.
there are quite a few old 737/727 freighters out there that will need replacement. And the A320 family has proven to be a workhorse.
But I guess It'd be sound to expect from someone to propose a freighter conversion of those before Airbus, if ever, designs a purposedly built a/c.
I'll do my own airline. With Blackjack. And hookers. In fact, forget the airline.