>Why work on scalability before SMTs and hf20 when we are never using more than 0,2% ?

I had the same question. Maybe theres are more problems regarding scalibility that doesnt necesarily relate to the blockchain capability. 
For example: the rapid grow in accounts creation vs. the physical cost of creating each account + the low user retention in the platform.
Those are problems with scalability even tho if they dont represent an overload in the system. 
Just a guess, but i would love to have a certain answer. 
Thanks for adressing these problems, @runicar.
D.