I thought that Airbus tweaked the software after the Air Transat glider incident to flag warnings if consumption was more than it could explain? Or was that just for leaks, and engines working harder than expected take an amount of fuel that is considered acceptable based on control settings?
It sounds like they could do with another tweak to at least display that at current fuel consumption rate (averaged over five minutes, perhaps), the target number of miles won't be reached. It shouldn't actually be that hard for it to flag standard reasons why, such as climb, headwind, excess bits hanging out causing drag, etc, as I'm sure the FMC normally knows all this.