I think the whole 'blades that may shatter are not permitted' thing becomes much less important when the arena is a bulletproof box. That rule has been in there for as long as I can remember and was surely written at a time where spinners were running in arenas with fabric roofs.

The debris thrown about in Robo Challenge battles can be pretty intense yet it is always contained safely. If a saw blade was to shatter in that arena, I would trust the robustness of the arena to contain it. For any wooden class battles at the FW champs, if Robo Challenge are comfortable with the security of their arena and are happy to allow saw blades, then they should be permitted for this event as they would be a good source of destruction in that class. Obviously any wooden class battles in the RR or RL arenas would have to meet the 'no spinners or hardened blades' criteria.