There is no doubt Airbus are working extremely hard to determine the root cause, the future of the 225 depends on it. Honestly, Airbus's future in the O&G world largely depends on it. Frankly these days, they are probably better off putting their efforts else where anyway, the O&G world is so cut throat, they will soon be expecting operators to pay to fly for them.
One thing that has struck me a bit odd is all the design questioning. All the load anaylsis, material anaylsis, cycle counts, bearing types, rotation counts, number of blades, number of suspension bars, weight reductions, power increases, and on and on ........All, over the top blabbering IMO ...... The L2 flew for how many years? About 18-19 years before that gearbox failed. I don't care who you are, after almost 20 years of operation of any mechcanical item, do you go straight into believing there is a design flaw or a structural integrity problem? Probably not! The next similar failure of the same component, 7 years later, 25-26 years after design and about 12 years into the 225 life .... Design problem? Again, probably not.
We all know they have a problem and Airbus knows they have a problem. Have they probably found a common denominator with the one bad planet gear manufacturing? Has something changed in the manufacturing of that gear ... It's been working for 20 years? Was that part number available from design conception or was it brought into play XX years after gearbox design to keep up with demand? If yes to any of the above, is removing them from service and just running the more reliable gears an acceptable solution? Maybe the later coupled with the lower TBO and increased maintenance monitoring (10 hour chip and filter inspection) is enough? Maybe there could have been rough handling of the gearbox? Could there have been a maintenance error? In my opinion, all valid questions and probabilities ... None that seem anymore or less out to lunch then a poorly designed gearbox that managed to work faithfully for 20 years. Some have been ruled out while they continue to hammer away at others I'm sure.
Unfortunately, no matter what cause is determined, they will probably never be able to convince us that enough is done .... The pure nature of the accident, fatal with little to no warning (I says this lightly, REDL did try to throw some failure indicators in time), makes the solution hard to swallow.