Streaming is an important c++ feature
Although it is an important c++ it does not imply that it should be a key feature of Arduino.
The ''stream insertion operator'' << and >> which actually is bit shift operators have caused quite a few discussions, and even more questions.
Many people find them cryptic, I've always though 'shift all the bytes of the string (or the object) into' whatever happenes to use/call the operator << or >>.
I think teaching function calls is better, and it looks cleaner, than stream insertion does. Although it results in longer code.
Streaming makes printing text easier and the library is efficient, it generates no extra machinecode.
I hope the Arduino staff will add this library to the Arduino core or to the Contributed Libraries[ch8221] list.
Although I've mostly argued against I agree.