very nice bloghttp://developer.mbed.org/blog/entry/20-shields-on-10-st-nucleo-platforms/by @Mihail Stoyanov mbed announcing that 20 shields are now fully supported and tested across 10 STM32 Nucleo platforms on mbed.
ST had been first partner to use the mbed automated test suite for platform support development on mbed and through it set a quality acceptance criteria for a target support in the mbed SDK.
have also a look to STM32 Facebook page