I still haven't updated since 3.15 and its really starting to kill me. I don't want to risk losing Linux just for PSGroove at this point in time although I pretty sure they'll find a way to incorporate it down the road or a least a method to downgrade.
i dont think it would be as simple as just coppying the files over and hoping they will work (probably end up with a brick...) with more annalasis on older firmwares we can see where there have been patches to lvl0, lvl1, lvl2 then we can work on reverse engineering the firmware even patching CFW so that we have linux or ps2/ps1 BC.
It's just a sweet matter of time. This feels just like it did back in the early days of the PSP.... ahh the fond memories. I just wish my kids did not update me from 3.15 but it's cool I am happily at 3.41 atm and could not be happier, tough linux would be nice to get back. Another thing to be thankfull is that my ancient Fat has not ylod on me so as far as PS2/PS1 goes I can still play those, but if my fat ever dies getting that back would be nice.