It's not a big deal, but it does make you question the utility of having the secondary SoC vs. just having a standard southbridge. I guess it does still relieve some memory/processing overhead from the main system. I'm more baffled that they couldn't make it work as originally intended.
I think it would be interesting with some of the low-level knowledge of what Sony intended to say whether this scheme saves much processing overhead in a more standard arrangement than the PS4.
A big chunk of what it's doing is abstracting IO, acting as the handler for system devices, running its own OS, quality of service, and storage management/encryption. That can be decently complex, but from the looks of things it is doing a lot of work because Sony wanted this work duplicated and run through its esoteric system architecture.
How much of the work "saved" from the main system just wouldn't be there if the attempt at saving it wasn't made isn't clear.
The PS4 jailbreak seems to indicate that Sony had some oddly roundabout ways of getting things done, and part of its flaky security model is to apparently baked into the isolation of the APU and its OS from a lot of this work.
Given the limited power of the southbridge, Sony may have underestimated the performance needed for timely handling of data, decrypting, firing up devices, processing, running its OS, re-encrypting, and installing updates.
This could be doable with the chip in question, but perhaps not in the case of doing so when this chip is also navigating the system hierarchy that is also plugged into an x86 chip, suspend mode, and yet another OS--all of which might need to be updated from an arbitrary version, partly active, or could be woken up at very inconvenient times.
Perhaps that could be doable, but perhaps not without system software that is sufficiently robust or optimized, and Sony's shown signs that they are not fully up to that task.
Further up from that, it might not be within Sony's grasp to be able to get even a non-optimized but functional software stack for background updates.
The wake-up process, system management, and network+install processing stack for the PS4's fully-on APU mode is by necessity the one that already needs to be functional, and it has the performance to help brute-force kludgy workarounds--and that is the one path they could get to work. There's possibly more help available in the side of the system that has more standard hardware and isn't wholly super-proprietary.
The PS4 hack wasn't that complimentary on the quality of Sony's work. (edit: the presentation on it) Some of it was bewilderment which might not be entirely fair in its evaluation of what Sony was doing, but there's a lot that seems to be band-aids and less than successful internal development going on.
