The GXR system is an excellent system but lacks the range of modules (at the moment) to show why it's so good and where it's advantages lie vs a normal interchangeable lens system.
I have tried to explain the system and it's advantages a bit here:
Cristian Sorega Photography: Ricoh GXR Review - GXR System, Body & Controls
But what it boils down to is in my opinion this:
The GXR system is not a camera system but more a digital modular system that does not need to have anything at all to do with cameras as such. The system is simply the ability to connect a control module to a system module and being able to swap these system modules in order to get the best one for the task at hand. The GXR system can be anything Ricoh desires it to be by simply building the body and system modules required for a specific task.
Still, even at the moment the greatest advantage is as usual with Ricoh, the exchellent controls and thought out frmware that makes it easy to customize the camera to a degree that one can control it without even going into menus or even looking at the screen.
I'm looking forward to hearing/reading more from you, Andrew! Does "A12" refer to the APS-C sensor? It's confusing that there are 50mm and 28mm units, both called "A12".
This I did not put in my review above but it works basically like this:
The A stands for APS and 12 for the MP so 12MP followed by the focal length 28mm or 50mm.
The S10 means it's a small sensor with 10 MP followed by the focal length again 24-72mm and VR for image stabilization.
The P10 is where it gets difficult since it also has a small sensor with 10MP but here it's more for point&shoot with limited manual controls (no full aperture controls for example, only 2 steps) and an even smaller sensor.