We have this idea in mind for future versions, but right now, it's not possible to load an application from the SD card (only or FLASH).
The diffulties are:
Today, the application is relocated at its final address (in FLASH). Within a uSD, the solution would be to copy the application to a fixed address in RAM, or to a fixed address in FLASH (but we would have to erase/reprogram the FLASH before launching any application). But why not...