Unfortunately nobody here is a mindreader, so until he publishes his "theories" it would be a waste of time to speculate on tweets like that.
Edit: I see he has now updated his blog with more specific details, as follows:
On the Isolated SPUs
Today I verified my theories about running the isolated SPUs as crypto engines. So to people like this, sorry you are wrong.
In OtherOS, all 7 SPUs are idle. You can command an SPU (which I'll leave as an exercise to the reader) to load metldr, from that load the loader of your choice, and from that decrypt what you choose, everything from pkgs to selfs. Including those from future versions.
The PPU is higher on the control chain then the SPUs. Even if checks were to be added to, for example, verify the hypervisor before decrypting the kernel, with clever memory mappings you can hide your modified hypervisor.
Ah, but you still didn't get the Cell root key. And I/we never will. But it doesn't matter. For example, we don't have either the iPhone or PSP "root key". But I don't think anyone doubts the hackedness of those systems.
I wonder if any systems out there are actually secure?
So basically he's saying according to his research iQD's theory isn't correct is all.
George states that you can decrypt pkgs, would I be right in thinking that includes the files extracted from updates? If so then I'm guessing it would make it easier for people to analyse the firmware for possible "bugs"
What i get from his update is the now he can command/force any of spus to decrypt any pkgs or selfs and even modified/make a custom hypervisor would it means he can run unsigned code or maybe i'm all wrong.