OpenRex is in assembly house and we are expecting prototypes within two weeks. Fingers crossed.
I attached an idea of OpenRex supporting add-on boards. The TOP OpenRex add-on board is also Raspberry Pi compatible. It may be used on the OpenRex SOLO version (with no or low profile heatsink). The BOTTOM add-on boards are larger. The plan is to support multiple add-on boards stacked on top of each other. It will require a lot of testing and playing
This is a 3D PDF, use Adobe reader to have a look at the board in 3D view.