This is may be a cosmetic issue; but trying to run Arduino sketches that are using the new Arduino (1.5.8 and upward) SPI library gives compilation error because the SPI.usingInterrupt() function is not implemented in the ESP8266 one.
I don't know exactly the impact and this function is maybe irrelevant for the ESP environment, however for compatibility reasons, a dummy function could may be implemented allowing transparency, between the SPI libraries
Robert