Hmm... sounds like a hybrid firmware: Must install from 3.55
PUP packed with 3.55 means no private keys. Public keys like appldr and such can be found it's just a matter of method but the VSH must be mixed since with a 3.55 CFW. If anyone remembers... Naima of Elotrolado created a 3.60 hybrid firmware that allowed PKGs to be installed and both be on PSN. moja of PS3News also did it.
for sure they would have to use a hardware flasher to make this firmware and to test it, so they don't actually need to show the HW as it wont be required when/if it finally gets released.
i was hoping that someone found a root exploit to allow the installing of a modified firmware (whether it be custom firmware or hybrid firmware) but that seems to not be the case as it is a Dex convert so it'll almost certainly still only be for 3.55 peeps.
personally as my machine is already 4.21 i wont be able to install it anyway unless they have found an exploit but i'm getting the new Progskeet as soon as is possible, so it wont be an issue either way.