Speakers: Anything really new under the sun?

I would say that it's down to refinements of existing technologies and passive components for crossovers. I believe that with all of the time that's passed, the ultimate success of any speaker is down to the talent of the person or persons who voice the speaker, even though of course the final sound is partially dictated by the room that it's used in.

I think all the basic technologies were developed decades ago, electrostatic, ribbon, AMT, dynamic… etc. But the progress of implementation has simply been a game changer; continued incremental improvement. I was in love with electrostatic and the ribbon speakers for over 30 years …   but after 10 years of listening to live acoustic music realized why traditional dynamic speakers are the most common. They are capable of reproducing the most realistic musical sound… and decade after decade of advancement has made a huge difference in their ability to present coherent and musical output… as opposed to some exaggerated and magical sounding aspect. Advances in building enclosures, drivers and crossovers has been phenomenal. You can see my systems under my UserID.

The biggest step forward was the improvement in the crossover parts quality. Mainly massive leaps in capacitor technology are responsible for most of the sonic improvements we hear over 20 years ago. Basically, take a top speaker from 20 yrs ago, change crossover parts to current high quality parts (caps, resistors, inductors, wiring, solder), and it will compete at the same level as top performers today.

AKA: you have a 20-30y old speaker you love, just bring the crossover up to our age, and you have arrived.

There was a trend though in the past 20 yrs: the voicing moving away from high fidelity to high end. That is, from a balanced natural sound towards a bigger show, enhancing apparent detail level at the cost of compromised tonality.

A second strong trend of the past 2 decades: loudspeakers are getting harder to drive, impedances are sinking lower, forcing you towards solid state amplification.  This provides lesser dynamic range and dependency on very high damping factor and high wattage.

A very few speakers from 20-40 years ago had no resonant cabinets.
But even today there are a lot of speakers with cabinet resonances.

There are a very limited number of cones that do not distort and changes shapes as breakup modes.

Some motors are more linear, but not every manufactures uses those… only a few.

Diffraction is better understood, but there are still lots of cabinets where diffraction is an issue.

Good designs from the past are still good today, and many speakers today and heavy on the marketing.

I think advancement in speakers is similar to advancement in other electronics like TVs and computers.  Many things are similar and there's amazingly good speakers at reasonable price points.

The higher in price you look - the companies have invested in computer modeling, material science efforts resulting in step change improvements.  A $500 speaker 10-20 years ago will not hold a candle to many of the $500 speakers of today.