Machinbird:
I think what Airbus needs to do is set the probability of triple airspeed failure = highly probable in their analysis, and then modify their systems so that such events are ho-hum non-events.
This will not be inexpensive.
... They have to be already looking at this question and cringing at the cost.
Your analysis is convincing, however there might be another option.
What would have happened if the pilot was warned of the
imminent pitot-tube failure and then flew the plane appropriately for unreliable-airspeed [e.g. flying attitude & power]?
Would this have kept the wolves at bay until the plane was out of the ice-crystal conditions? Would a few false alarms in severe ice-crystal conditions be acceptable?
If so, don't we have the much cheaper option of designing a pitot-tube that reports when its heater is being overwhelmed ... and integrating this information into the AB display.
Regards, Peter
As well as providing early warning of imminent failure, a smarter pitot-tube could also provide maintenance-level feedback of the thermal headroom actually available in flight.