For evidence, how many successful Airbus P2F conversion programs have there been? One, the A300.
Actually a fairly large number of A310 P2Fs were done as well, although mostly to Fedex. There is/was a conversion programme for the A320P2F, but it has been shelved for the time being not because it isn't popular, but because the A320 is so popular with airlines that there is not enough feed-stock to keep a P2F conversion line up and running! They have just launched the A330P2F, although they are going to have difficulty finding feedstock for that as well because of the A330s popularity. (They launched it mainly to appease Qatar's CEO who threatened to buy a large fleet of 767Fs). Similar story for the A340, there is not enough feedstock to make a conversion line viable although there is a third party who are about to launch their own non-permanent P2F programme for the A340-300.