Nice article, one should also be aware that keyword questions are becoming more important. Keyword questions are being driven by the uptake in search driven by voice on Siri and Cortina. With voice search people ask questions rather than look for keywords so as an example rather than type Plumber London they will say find me a plumber near me in Westminster to fix my boiler.

The difference being voice uses natural language questions and this optimisation needs to be done for this type of question.