So far all I've heard is probes into stuck gas pedals and software review. Of course, if the problem is not a stuck gas pedal then the assumption is the hardware is fine. If the software is tested thoroughly, then it too must be fine and the problem doesn't exist. Yet, something is happening.
Having been involved in the hardware and software investigation of very intermittent problems, it's not surprising to see these discussions. This happens when the vendor doesn't really want to find the problem, but rather put the blame elsewhere.
There are other sources of problems, and they can be difficult to replicate and even harder to fix. The two most common areas I've experienced have been timing and interference. Timing issues can be anything from handling of interrupts out of sync with clocks or other code. Interference can affect sensors or logic levels from external RF energy, electrostatic discharge, or noise from in-circuit inverters. Interference is the toughest because the source that happens in the field doesn't always exist in the lab.
The possibility of interference as a source of the problem is also a hard pill to swallow for some engineers because they tend to trust shielding that is either insufficient or not properly installed, thus making it more of an antenna and transformer of energy rather than protecting the equipment from that energy. Elimination of the source of the energy at the hardware is one method of solving the problem, but it doesn't hurt to have the proper software rules in place to insure that exception conditions are handled properly (for instance, you shouldn't need to press the brake and accelerator to force the vehicle to slow down. When the assumption is the accelerator is stuck and you only try to press the brake, nothing happens because the accelerator isn't actually stuck... duh).
Instead of testing such narrow parameters for the situation to appease Congress, Federal officials, and Toyota Management, a broader scope should be done. The quickest way would be by Toyota engineers who have knowledge and access tot he internals, but if they cannot be open minded about it then a third party with full access to the designs might be in order.
I see the long term results of this strategy similar to electricity and phones. Companies can not arbitrarily turn off your phone without a valid arguement that can withstand courts.
Some Internet connections may already be in this situation, although it has not been tested in court AFAIK. There are a number of people whose sole phone access is through their broadband Internet connection (such as Vonage or Time-Warner). These telephone providers already have the burden of providing 911 service, so why not lifeline service also?
My sister opened a computer store in Hawaii. She sells C shells down by the seashore.