Falcon 64

I know, Paul..
The willingness of the rudderstabs! to flutter is a harder task to solve.
The cure is better bulkheads of course and wider distance between the carbon shafts (wich will lift the level of reconance). Rigidity as the R/stab structure itself, a third case.
As I know it, flutter in the R/stabs have not yet been an issue? And I assume therefore they aren`t the problem. That brings us back to the main-issue, the elevons with the HC bulkheads.
IF you fly the Tomcat as it is out of the box, I`m not surprised it would come down after a number of flights. The subject you mention aeroflexibility, is the core here. Because the elevons are constantly trying to outlive it`s own world, wich is fluttering wildlessly. This create a incredible amount of torcue and it`s never brought to silence since they have not all elements of it to do so. AND this constant factor of an attempt to flytter is the cause to build enough slop in setup AND components such as alu servo-rigs and so on. When big enough, the linkage, slop in servo, bulkhead or any other loaded component WILL fail. And it might not be noticable for the modeller to discover it before it`s too late. That`s how big these forces are. If we could measure the amount of torque created by the elevons before and after balancing, it would be a jawdropping experience..
Then we have you last element in your post, the structure rigidity of the fuselage in roll, the need to give up on twisting forces when using the elevons as ailerons. If that really is a issue with the huge span of the tailerons, the bulkheads must be soft as biscuit, and perhaps it is.
Solving that can`t be done another way than making the formers/bulkheads stiff and strong enough with mass in them, but since we can take the main issue away, it also reduces the stress to a minimum, meaning the stress there is left is another world than before.
I DO NOT defend FEJ in making bulkheads behind trailing edge out of HC, misunderstand me correct!..
They should be made of the highest quality ply with carbon on both sides (like my big FEJ F-16), nothing less on a model in this size and type. Since mine just came with that, I also assume this is the way they always will make them from now on. Meaning they are listening..

One more thing, the big FEJ F-18 which masterly landed lately, was saved just because the bulkheads was made of ply, and of course a expert pilot.
But then again, this plane was not either balanced...or am I wrong? Don`t think so.