I worked for a BLDC company in their research division for a few years and there are many things that can still be improved. At the time we were working on reducing the size of motors without sacrificing torque or efficiency. This was particularly the case for industry motors where we developing a motor half the size of an older industry standard AC motor, but with the same power and 94% efficiency.

Size is where the majority of advancements for BLDC motors will come.

Advances in size and weight is what will enable innovation in new applications of motors.

Any names, journals or textbooks about the subject ?

Reading from other comments: the 95% efficiency in "traditional" motors is only reached in ideal, fixed conditions (in terms of speed and torque). New advanced control systems increase efficiency at different speeds/torque.

Accurate! For many applications it was considered irrelevant and motors were just wound for a fixed speed. Outside this range the efficiency can drop drastically, below 50% for some motors (hence why shunt-wound motors were once used).

Well, i can see a point in continuous R&D. Maybe they could improve something else beside efficiency? Like size, weight, cost?

Let them study all the things!