Opus is a remarkable codec because it’s excellent at almost everything. The only areas where it’s being beaten are extreme narrowband, which it can’t do, and narrowband, where it’s still not shabby (though some of this new stuff is redefining what’s possible).
Opus tackled a broad field of competitors that were each somewhat specialised for their part of the field, and pretty much beat all of them at their own game. And in most cases the incumbents were high-latency, while Opus not only achieves quality superiority but also supports low-latency operation.
https://en.wikipedia.org/wiki/Opus_(audio_format) has some good diagrams and explanation. https://upload.wikimedia.org/wikipedia/commons/8/8d/Opus_qua... especially shows Opus’ superiority except in narrowband.
Past about 16kb/s, Opus is pretty much just the format to use, except for extreme niches like if you want to represent over 20kHz (above which Opus cuts).
Opus is so good there’s pretty much nothing left to improve for now (for now), and even if you improved things it probably wouldn’t be worth it. That’s why all the development is happening in narrowband, because that’s the only interesting space left. Perhaps eventually some of those techniques will be scaled up past narrowband. I don’t know.