I'll have to look into the details so more; it looks like its exending some ideas that are already around.
For example, TI"s BoosterPacks are already processor independent (TI makes MSP430, Tiva ARM, Hercurles ARM, and C28x DSP Launch Pads).
The plug in modules appear similar to exsting peripheral connection standards such as PMod, Grove, TinkerKit, microBus, Gadgeteer, and UEXT, all of which are processor independent. One big plus is the sheer number of boards that can be plugged in; stacking shields, capes, or Booster Packs takes a lot of care (and often isn't possible).
Thanks for the terrific article Alan. We are already looking ahead to our next product offerings.
E3 Embedded announced on 9/3/14 our plans to offer both an AVR processor board and support for an embedded Linux processor board in 2015. The AVR board will be an E3 Embedded design while the Linux board will be an adapter to permit a currently available Linux embedded processor to interface with the PIEP motherboard. The AVR processor will be based on the ATMegX chip. Selection of the Linux processor board is to be determined, but will most likely be a SO DIMM form factor with high speed functions (HDMI, USB) terminated on the E3 adapter; remaining I/O brought out to the PIEP peripheral interconnects. We look forward to bringing these, and other exciting products, to market over the comming months.