Without seeing the serial console output I can't help in determining why it didn't boot from USB media.
It can be as simple as building your own booting RFS, and then copying my binaries over - you can do that by loopback mounting partitions inside the image I've provided, or imaging to actual SD card and mounting / copying the files you want off partitions.
As far as the SoC and what the hardware supports, its easy - you know my kernel rev, and you can google the chipsets in the PP, so see if they are supported - Linux is pretty agnostic hardware wise as long as its in the kernel it just 'works' usually. What the hell does a PBX need eSata ports anyway
NOW all this being said, it is VERY limited what I can do supporting anything beyond a SheevaPlug, and I'll tell you why....
1) This website I host with my own money. No ad-revenues or other income, Donations I ask for without conditions, but so far this hobby is costing me money
2) The hardware I've purchased comes out of my own pockets, donations don't cover my costs there either
3) I'm not getting paid to do this work, or compensated. In fact, I've discovered at least one other person attempting to sell PlugPBX outright without me seeing any kickbacks, which well honestly, it leaves me with a bad taste in my mouth - In fact, trying to charge seat licenses for what has none already, is just stinky.
So why should I put myself out another $150 bucks for a GuruPlug? So for right now, I'm limited to what I can offer direct support wise. I just bought a third SheevaPlug so I can start work again since taking down my in-use units is too much of a pain.
I would speculate, since GuruPlug is a new revision, there will be some initial growing pains, but very quickly it'll be easy to support. With enough time and energy I could even perhaps build a NAND version of PlugPBX - but again, time, money, justification...
Post a dump of your serial console while it tried to boot from your USB key, can't make any progress unless we listen to what its saying during bootup
Basically, you have to keep digging, don't give up the first time you try something, get your hands dirty. I'd have not gotten PlugPBX going if I gave up first trial
Everything is possible, and what I've provided can be distilled and re-used on the GuruPlug - I'm certain of it.