It would be interesting if a pro company could possibly make something more sensitive but play lower. I know there are lots of compromises because you're fighting physics the entire way, but the market is RIPE for it.
That's like saying
"I wish Ford could make a Mustang that goes faster and gets better mileage."
These two things are mutually exclusive.
For instance, the B&C 8NW51 packs a TON of neodymium into the motor, raising the efficiency by a few dB in the midrange, but at the cost of output at lower frequencies.
Basically as you raise the motor force you get a higher efficiency, because efficiency is determined by motor force and mass. But as the motor force goes up, QTS goes DOWN. The B&C 8PS21 has 5dB more output at 100Hz than the 8NW51, but the 8NW51 has more output in the midrange.
This can be compensated, by putting the woofer in a back loaded horn, but it definitely makes things more complex. It takes a lot of money and effort to 'eke out' a couple dB more in efficiency. And in an era when amplifiers are basically free, it's hard to justify that.