Why? I ask only for technology that was already availlable 2/3 years ago on flagships about the same price (around 450€ for 808...) ?

What could also happen is that another bigger manufacturer (I like Sony with its Xperia Z range) can do something like this and put Sailfish OS on it. This would still be a win for Jolla by licensing Sailfish.
Still, no one ever made a good camera phone with HW keyboard, and manufacturers forgot that there was a time where high range phones had screens between 3.5" and 4"...