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.