Its actually that sort of statement (lacking context) that was debunked by both the Purdue and Liverpool university tests of 2008/2009, its true if you have a drink with nothing else for 6 hours, but any other food stuff drunk within 2 hours will have more of its sugars absorbed by the body than had you drank water by comparison.
There is more to a diet than just carbs and this is born out by the study of 7500 soft drink consumers using diet drinks over 5 year by the University of Texas, one diet soft drink a day results in a 65 percent increase in the chance you are more likely to become overweight during the next seven to eight years.
I am not sure that one drink a day is in moderation.
You are right to say there has been no credible research that has been done long term, but if we have a look at what has been done there is already problems:
Coke Zero uses Acesulfame K which does contain the carcinogen, methylene chloride.
Coke Zero also uses Aspartame and to quote the the US Governments NIH website "Our study shows that Aspartame is a multi-potential carcinogenic compound whose carcinogenic effects are evident even at a daily dose of 20 mg/kg bw, much less than the current ADI for humans in Europe (40 mg/kg bw) and in the United States (50 mg/kg bw)."
First Experimental Demonstration of the Multipotential Carcinogenic Effects of Aspartame Administered in the Feed to Sprague-Dawley Rats
Qantas have given people another drinking choice - is it more healthier than others (excluding H20), I am not sure, and its an individual choice whether to consume it, but its not the "healthy choice" on the cart IMHO. I might add I do not have any shares/financial interest in any sugar or soft drink producer, I am still paying the price of having been a less educated consumer in the past when it came to processed food consumption, often as a time poor frequent traveler.