Hmm. I don't know anything really about this. But it surprises me that nobody has publicly attempted to bruteforce the private keys and explain their results.
Why would anyone want to do that? Well it could make a good exercise towards a CS degree or university thesis in computer security and cryptography. Most of the work would be to write the necessary program to run on some modern GPUs. Or re-working such a bruteforce program that already exists. Obviously, set it up to try a small sample like 100 keys or 1000 keys, whatever make sense. Then calculate based off the sample time what's required to go through the entire search space.
If that sounds like a waste of time - it isn't. Eliminating this method. It is a great way to push others to think harder about the remaining possible routes: Since no-one will be waiting, hoping for someone else to find another shortcut to get the private keys. Lots of people say it, and its kindda obvious. But no-body actually *proves* it.
Then you are left with an unpatched exploit, the debugging tools, attacking the hardware directly, leaks from within Sony, etc. Still a fair few possibilities. Just nobody wants to work on them since they had it so easy up till now! Well that is a joke, clearly. The PS3 has been without any doubt the hardest console to crack of all time.